feat(mcp): local MCP server exposes voicebox.* tools to AI agents

Mounts FastMCP at /mcp (Streamable HTTP) so Claude Code, Cursor,
Windsurf, and the VS Code MCP extensions can call voicebox.speak,
voicebox.transcribe, voicebox.list_captures, and voicebox.list_profiles
against the running Voicebox server.

Backend
- new backend/mcp_server package (tools, middleware, profile resolve,
  pub/sub events); named mcp_server to avoid shadowing the installed mcp
  PyPI package FastMCP imports internally
- app.py migrated from @app.on_event to lifespan= so FastMCP's session
  manager cohabits with Voicebox's startup/shutdown
- new MCPClientBinding table + /mcp/bindings CRUD; ClientIdMiddleware
  reads X-Voicebox-Client-Id into a ContextVar and stamps last_seen_at
- profile resolution precedence: explicit -> per-client binding ->
  capture_settings.default_playback_voice_id
- POST /speak REST wrapper for non-MCP callers (shell, ACP, A2A)
- GET /events/speak SSE broadcasts speak-start / speak-end so the pill
  surfaces agent-initiated speech
- backend/mcp_shim proxy (plain httpx) for stdio-only MCP clients
- PyInstaller spec updates + new --shim build target (~18 MB)

Frontend
- Settings -> MCP page with HTTP / stdio / claude-mcp-add copy snippets,
  default voice picker, per-client bindings table, connection status
- useMCPBindings, useSpeakEvents hooks
- CapturePill gains 'speaking' state; DictateWindow subscribes to SSE
  and emits dictate:show so the Rust side surfaces the pill window

Native
- tauri.conf.json externalBin now includes voicebox-mcp
- show_dictate_window helper + dictate:show listener in main.rs
- (also in this commit: InputMonitoringGate UX, hotkey_monitor tweaks,
  landing footer/navbar updates, new overview docs for captures /
  dictation / mcp-server / voice-personalities)

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

app/src/router.tsx

@@ -17,6 +17,7 @@ import { GeneralPage } from '@/components/ServerTab/GeneralPage';
 import { GenerationPage } from '@/components/ServerTab/GenerationPage';
 import { GpuPage } from '@/components/ServerTab/GpuPage';
 import { LogsPage } from '@/components/ServerTab/LogsPage';
+import { MCPPage } from '@/components/ServerTab/MCPPage';
 import { SettingsLayout } from '@/components/ServerTab/ServerTab';
 import { Sidebar } from '@/components/Sidebar';
 import { StoriesTab } from '@/components/StoriesTab/StoriesTab';
@@ -159,6 +160,12 @@ const settingsCapturesRoute = createRoute({
   component: CapturesPage,
 });
 
+const settingsMCPRoute = createRoute({
+  getParentRoute: () => settingsRoute,
+  path: '/mcp',
+  component: MCPPage,
+});
+
 const settingsGpuRoute = createRoute({
   getParentRoute: () => settingsRoute,
   path: '/gpu',
@@ -204,6 +211,7 @@ const routeTree = rootRoute.addChildren([
     settingsGeneralRoute,
     settingsGenerationRoute,
     settingsCapturesRoute,
+    settingsMCPRoute,
     settingsGpuRoute,
     settingsLogsRoute,
     settingsChangelogRoute,