feat(claude-desktop): add 3P provider switching with proxy gateway

Adds a new ClaudeDesktop AppType that writes Claude Desktop's third-party
inference profile under configLibrary/, sharing _meta.json with other
launchers (Ollama-compatible) so cc-switch can coexist with them.

Two switch modes:
- direct: provider already exposes claude-* / anthropic/claude-* model
  ids on Anthropic Messages, Claude Desktop connects to it directly.
- proxy: cc-switch's local proxy acts as the inference gateway,
  presenting only claude-* route names to Claude Desktop and mapping
  them to real upstream models. Required after Anthropic restricted
  Claude Desktop to claude-family ids.

Backend:
- New module claude_desktop_config with snapshot/rollback, official seed
  bypass, /claude-desktop/v1/{models,messages} routes, and a single
  source of truth for default proxy routes.
- Gateway token persisted in SQLite, validated on every proxied request.
- get_claude_desktop_status surfaces drift signals (stale models,
  missing routes, proxy stopped, base URL mismatch, missing token).

Frontend:
- Slim ClaudeDesktopProviderForm independent from ProviderForm,
  controlled by a top-level appId guard.
- ProviderList banner consumes the status query (5s polling) and
  renders actionable diagnostics.
- ClaudeDesktopRouteToggle in the header to start/stop the local
  gateway without touching takeover state.
- Three-locale i18n synchronised.

src/components/common/AppCountBar.tsx

@@ -5,7 +5,7 @@ import { APP_IDS, APP_ICON_MAP } from "@/config/appConfig";
 
 interface AppCountBarProps {
   totalLabel: string;
-  counts: Record<AppId, number>;
+  counts: Partial<Record<AppId, number>>;
   appIds?: AppId[];
 }
 
@@ -27,7 +27,7 @@ export const AppCountBar: React.FC<AppCountBarProps> = ({
             className={APP_ICON_MAP[app].badgeClass}
           >
             <span className="opacity-75">{APP_ICON_MAP[app].label}:</span>
-            <span className="font-bold ml-1">{counts[app]}</span>
+            <span className="font-bold ml-1">{counts[app] ?? 0}</span>
           </Badge>
         ))}
       </div>

src/components/common/AppToggleGroup.tsx

@@ -8,7 +8,7 @@ import type { AppId } from "@/lib/api/types";
 import { APP_IDS, APP_ICON_MAP } from "@/config/appConfig";
 
 interface AppToggleGroupProps {
-  apps: Record<AppId, boolean>;
+  apps: Partial<Record<AppId, boolean>>;
   onToggle: (app: AppId, enabled: boolean) => void;
   appIds?: AppId[];
 }