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/routes/links.py

@@ -3,9 +3,10 @@
 import logging
 import re
 from typing import Any
+from urllib.parse import urlparse
 
 from fastapi import APIRouter, Depends, HTTPException, status
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, field_validator
 
 from ..auth import verify_token
 from ..config import LinkConfig, settings
@@ -15,6 +16,35 @@ from ..services.websocket_manager import ws_manager
 router = APIRouter(prefix="/api/links", tags=["links"])
 logger = logging.getLogger(__name__)
 
+# Only allow MDI iconify slugs and safe `http(s)`-ish URLs through the API.
+_MDI_ICON_RE = re.compile(r"^mdi:[a-z0-9][a-z0-9-]{0,63}$")
+_ALLOWED_URL_SCHEMES = {"http", "https"}
+
+
+def _validate_url(url: str) -> str:
+    """Ensure the URL is well-formed http(s) — no ``javascript:`` etc."""
+    parsed = urlparse(url)
+    if parsed.scheme.lower() not in _ALLOWED_URL_SCHEMES:
+        raise ValueError("URL must start with http:// or https://")
+    if not parsed.netloc:
+        raise ValueError("URL must include a host")
+    return url
+
+
+def _validate_icon(icon: str) -> str:
+    """Restrict icon names to safe Material Design Icons slugs."""
+    if not _MDI_ICON_RE.match(icon):
+        raise ValueError("Icon must be of the form 'mdi:<lowercase-slug>'")
+    return icon
+
+
+def _require_links_management() -> None:
+    if not settings.links_management:
+        raise HTTPException(
+            status_code=status.HTTP_403_FORBIDDEN,
+            detail="Links management is disabled. Set links_management: true in config.yaml to enable.",
+        )
+
 
 class LinkInfo(BaseModel):
     """Information about a configured link."""
@@ -29,22 +59,25 @@ class LinkInfo(BaseModel):
 class LinkCreateRequest(BaseModel):
     """Request model for creating or updating a link."""
 
-    url: str = Field(..., description="URL to open", min_length=1)
+    url: str = Field(..., description="URL to open", min_length=1, max_length=2048)
     icon: str = Field(default="mdi:link", description="MDI icon name (e.g., 'mdi:led-strip-variant')")
-    label: str = Field(default="", description="Tooltip text")
-    description: str = Field(default="", description="Optional description")
+    label: str = Field(default="", description="Tooltip text", max_length=128)
+    description: str = Field(default="", description="Optional description", max_length=512)
+
+    @field_validator("url")
+    @classmethod
+    def _check_url(cls, v: str) -> str:
+        return _validate_url(v)
+
+    @field_validator("icon")
+    @classmethod
+    def _check_icon(cls, v: str) -> str:
+        return _validate_icon(v)
 
 
 def _validate_link_name(name: str) -> None:
-    """Validate link name.
-
-    Args:
-        name: Link name to validate.
-
-    Raises:
-        HTTPException: If name is invalid.
-    """
-    if not re.match(r'^[a-zA-Z0-9_]+$', name):
+    """Validate link name."""
+    if not re.match(r"^[a-zA-Z0-9_]+$", name):
         raise HTTPException(
             status_code=status.HTTP_400_BAD_REQUEST,
             detail="Link name must contain only letters, numbers, and underscores",
@@ -90,6 +123,7 @@ async def create_link(
     Returns:
         Success response with link name.
     """
+    _require_links_management()
     _validate_link_name(link_name)
 
     if link_name in settings.links:
@@ -129,6 +163,7 @@ async def update_link(
     Returns:
         Success response with link name.
     """
+    _require_links_management()
     _validate_link_name(link_name)
 
     if link_name not in settings.links:
@@ -166,6 +201,7 @@ async def delete_link(
     Returns:
         Success response with link name.
     """
+    _require_links_management()
     _validate_link_name(link_name)
 
     if link_name not in settings.links: