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/static/js/callbacks.js

@@ -81,7 +81,7 @@ async function _loadCallbacksTableImpl() {
         `).join('');
     } catch (error) {
         console.error('Error loading callbacks:', error);
-        tbody.innerHTML = '<tr><td colspan="4" class="empty-state" style="color: var(--error);">Failed to load callbacks</td></tr>';
+        tbody.innerHTML = `<tr><td colspan="4" class="empty-state" style="color: var(--error);">${escapeHtml(t('callbacks.msg.load_failed'))}</td></tr>`;
     }
 }
 
@@ -121,7 +121,7 @@ export async function showEditCallbackDialog(callbackName) {
         const callback = callbacksList.find(c => c.name === callbackName);
 
         if (!callback) {
-            showToast('Callback not found', 'error');
+            showToast(t('callbacks.msg.not_found'), 'error');
             return;
         }
 
@@ -142,7 +142,7 @@ export async function showEditCallbackDialog(callbackName) {
         dialog.showModal();
     } catch (error) {
         console.error('Error loading callback for edit:', error);
-        showToast('Failed to load callback details', 'error');
+        showToast(t('callbacks.msg.load_failed'), 'error');
     }
 }
 
@@ -175,9 +175,10 @@ export async function saveCallback(event) {
         shell: true
     };
 
+    const encodedName = encodeURIComponent(callbackName);
     const endpoint = isEdit ?
-        `/api/callbacks/update/${callbackName}` :
-        `/api/callbacks/create/${callbackName}`;
+        `/api/callbacks/update/${encodedName}` :
+        `/api/callbacks/create/${encodedName}`;
 
     const method = isEdit ? 'PUT' : 'POST';
 
@@ -191,16 +192,16 @@ export async function saveCallback(event) {
         const result = await response.json();
 
         if (response.ok && result.success) {
-            showToast(`Callback ${isEdit ? 'updated' : 'created'} successfully`, 'success');
+            showToast(t(isEdit ? 'callbacks.msg.updated' : 'callbacks.msg.created'), 'success');
             callbackFormDirty = false;
             closeCallbackDialog();
             loadCallbacksTable();
         } else {
-            showToast(result.detail || `Failed to ${isEdit ? 'update' : 'create'} callback`, 'error');
+            showToast(result.detail || t(isEdit ? 'callbacks.msg.update_failed' : 'callbacks.msg.create_failed'), 'error');
         }
     } catch (error) {
         console.error('Error saving callback:', error);
-        showToast(`Error ${isEdit ? 'updating' : 'creating'} callback`, 'error');
+        showToast(t(isEdit ? 'callbacks.msg.update_failed' : 'callbacks.msg.create_failed'), 'error');
     } finally {
         if (submitBtn) submitBtn.disabled = false;
     }
@@ -212,7 +213,7 @@ export async function deleteCallbackConfirm(callbackName) {
     }
 
     try {
-        const response = await fetch(`/api/callbacks/delete/${callbackName}`, {
+        const response = await fetch(`/api/callbacks/delete/${encodeURIComponent(callbackName)}`, {
             method: 'DELETE',
             headers: getAuthHeaders()
         });
@@ -220,13 +221,13 @@ export async function deleteCallbackConfirm(callbackName) {
         const result = await response.json();
 
         if (response.ok && result.success) {
-            showToast('Callback deleted successfully', 'success');
+            showToast(t('callbacks.msg.deleted'), 'success');
             loadCallbacksTable();
         } else {
-            showToast(result.detail || 'Failed to delete callback', 'error');
+            showToast(result.detail || t('callbacks.msg.delete_failed'), 'error');
         }
     } catch (error) {
         console.error('Error deleting callback:', error);
-        showToast('Error deleting callback', 'error');
+        showToast(t('callbacks.msg.delete_failed'), 'error');
     }
 }