fix: comprehensive security, bug, performance, and UI/UX audit

Security
- Default bind 127.0.0.1; first-run bootstrap generates random api_token
  and refuses to bind non-loopback without auth unless explicitly opted in
- Path-traversal hardened: BrowserService.validate_path rejects absolute
  paths, drive letters, UNC, NUL bytes. /api/browser/{play,metadata,
  thumbnail} now require folder_id and a folder-relative path
- Pydantic validators on links: http(s) URLs only, mdi:<slug> icons only
- Scripts/callbacks/links create/update/delete gated by *_management flags
- Strict CSP, X-Frame-Options DENY, Referrer-Policy no-referrer,
  X-Content-Type-Options nosniff
- CORS locked to localhost:<port> + 127.0.0.1:<port> by default; configurable
- config.yaml writes atomic (tmp + os.replace) and 0o600 on POSIX
- Subprocesses spawned in their own process group / new session so timeout
  kills the whole tree (Windows CREATE_NEW_PROCESS_GROUP, POSIX
  start_new_session=True)
- Frontend XSS: monitor name + details escapeHtml'd; power button moved to
  delegated data-action handler; remote MDI SVGs parsed and sanitized
  (strip script/foreignObject/on*/javascript: hrefs) before innerHTML
- All dynamic URL segments now wrapped in encodeURIComponent

Bugs
- WebSocket reconnect: close previous socket before opening new, clear
  ping interval per-socket, clear reconnectTimeout up-front, retry on
  online/visibilitychange, try/catch JSON.parse
- Artwork fetch race: AbortController + generation guard
- _broadcast_after_open: initialize status, swallow per-poll errors,
  background tasks tracked in a strong-ref set with done-callback cleanup
- Audio analyzer: sticky _unavailable flag prevents infinite start/stop
  spin when no loopback device exists; cleared by set_device()
- Volume short-circuit cache invalidated when server reports remote volume
- Browser thumbnail race: per-folder generation counter + isConnected
  checks; aborts in-flight fetches on navigation
- Track-skip uses cached title instead of full WinRT status round-trip

Performance
- Linux MPRIS/pactl and /api/display DDC-CI handlers wrapped in
  asyncio.to_thread so blocking IO never stalls the event loop
- browse_directory moved off the event loop (SMB shares could freeze it)
- Windows status poll caches one asyncio loop per worker thread via
  threading.local instead of new_event_loop/close on every 0.5s tick
- broadcast() serializes JSON once and uses send_text to all clients
- Hourly thumbnail cache cleanup scheduled in lifespan (was never invoked
  — cache grew unbounded)
- Progress drag listeners attached only while dragging

Quality
- All asyncio.get_event_loop() in coroutines → get_running_loop()
- ThreadPoolExecutors shut down cleanly during lifespan teardown
- config_manager dedup: 12 near-identical methods collapsed onto generic
  _upsert/_delete helpers (~290 lines removed)
- Service worker no longer pass-throughs every fetch
- M3U playlist written via NamedTemporaryFile (no fixed-path symlink
  clobber race)
- __version__ now prefers live pyproject.toml in dev checkouts so
  pip install -e . users see the source-of-truth version, not the stale
  package-metadata version baked in at install time

UI/UX (Studio Reference)
- Green leftover focus rings (rgba(29,185,84,...)) all replaced with
  copper accent (rgba(var(--copper-rgb),...))
- Dialogs: square corners, copper top hairline, unified with editorial
  chrome
- .browser-item: transparent with copper hover border (was filled card)
- Audio device select uses var(--sans) instead of generic system font
- Mobile container padding tuned for ≤480px screens
- Breadcrumb home is a real <button> with aria-label; aria-current on root
- i18n: filled display.msg.power_*, execution.*, scripts.params.execute,
  callbacks.empty in both en + ru

media_server/config.py

@@ -1,6 +1,8 @@
 """Configuration management for the media server."""
 
+import logging
 import os
+import secrets
 from pathlib import Path
 from typing import Optional
 
@@ -8,6 +10,8 @@ import yaml
 from pydantic import BaseModel, Field
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
+logger = logging.getLogger(__name__)
+
 
 class MediaFolderConfig(BaseModel):
     """Configuration for a media folder."""
@@ -81,8 +85,35 @@ class Settings(BaseSettings):
     )
 
     # Server settings
-    host: str = Field(default="0.0.0.0", description="Server bind address")
+    host: str = Field(
+        default="127.0.0.1",
+        description=(
+            "Server bind address. Use 127.0.0.1 for loopback-only (default, safest),"
+            " or 0.0.0.0 to expose on the LAN (requires api_tokens to be set)."
+        ),
+    )
     port: int = Field(default=8765, description="Server port")
+    allow_lan_without_auth: bool = Field(
+        default=False,
+        description=(
+            "Allow binding to a non-loopback address with no api_tokens configured."
+            " Off by default to prevent unauthenticated LAN exposure."
+        ),
+    )
+    cors_origins: list[str] = Field(
+        default_factory=list,
+        description=(
+            "Allowed CORS origins. Empty (default) means only same-origin requests"
+            " from http://localhost:<port> and http://127.0.0.1:<port>."
+        ),
+    )
+
+    # Admin-grade operations (script / callback / link / folder create/update/delete).
+    # When True the same token used for read/play can also persist arbitrary shell
+    # commands. Disable to make the API read+execute only.
+    scripts_management: bool = Field(default=True, description="Allow scripts CRUD via API")
+    callbacks_management: bool = Field(default=True, description="Allow callbacks CRUD via API")
+    links_management: bool = Field(default=True, description="Allow links CRUD via API")
 
     # Authentication (empty = auth disabled, anyone can access the API)
     api_tokens: dict[str, str] = Field(
@@ -218,21 +249,25 @@ def get_config_dir() -> Path:
 
 
 def generate_default_config(path: Optional[Path] = None) -> Path:
-    """Generate a default configuration file with a new API token."""
+    """Generate a default configuration file with a freshly generated API token.
+
+    The token is written into ``api_tokens.default`` and printed to the logger
+    so first-run users can copy it. Subsequent runs preserve whatever the user
+    has set.
+    """
     if path is None:
         path = get_config_dir() / "config.yaml"
 
+    default_token = secrets.token_urlsafe(32)
+
     config = {
-        "host": "0.0.0.0",
+        "host": "127.0.0.1",
         "port": 8765,
-        # "api_tokens": {
-        #     "default": "your-secret-token-here",
-        # },
+        "api_tokens": {
+            "default": default_token,
+        },
         "poll_interval": 1.0,
         "log_level": "INFO",
-        # Audio device to control (use GET /api/audio/devices to list available devices)
-        # Set to null or remove to use default device
-        # "audio_device": "Speakers (Realtek",
         "scripts": {
             "example_script": {
                 "command": "echo Hello from Media Server!",
@@ -240,26 +275,38 @@ def generate_default_config(path: Optional[Path] = None) -> Path:
                 "timeout": 10,
                 "shell": True,
             },
-            # Add your custom scripts here:
-            # "shutdown": {
-            #     "command": "shutdown /s /t 60",
-            #     "description": "Shutdown computer in 60 seconds",
-            #     "timeout": 5,
-            # },
-            # "lock_screen": {
-            #     "command": "rundll32.exe user32.dll,LockWorkStation",
-            #     "description": "Lock the workstation",
-            #     "timeout": 5,
-            # },
         },
     }
 
     path.parent.mkdir(parents=True, exist_ok=True)
-    with open(path, "w", encoding="utf-8") as f:
-        yaml.dump(config, f, default_flow_style=False, sort_keys=False)
+    _write_yaml_atomic(path, config)
+    _restrict_config_perms(path)
+
+    logger.info("Generated default config at %s", path)
+    logger.info("API token (label=default): %s", default_token)
 
     return path
 
 
+def _write_yaml_atomic(path: Path, data: dict) -> None:
+    """Write YAML to disk atomically via tmp file + rename, with restricted perms."""
+    tmp = path.with_suffix(path.suffix + ".tmp")
+    with open(tmp, "w", encoding="utf-8") as f:
+        yaml.dump(data, f, default_flow_style=False, sort_keys=False)
+    _restrict_config_perms(tmp)
+    os.replace(tmp, path)
+
+
+def _restrict_config_perms(path: Path) -> None:
+    """On POSIX, ensure config file is readable only by owner (0600)."""
+    if os.name == "nt":
+        return
+    try:
+        os.chmod(path, 0o600)
+        os.chmod(path.parent, 0o700)
+    except OSError:
+        logger.debug("Could not chmod %s", path, exc_info=True)
+
+
 # Global settings instance
 settings = Settings.load_from_yaml()