refactor(text): extract shared summarization service with tts/note/notification modes

Move server-side summarization out of lib/tts/summarization.js into a shared
lib/text module exposing tts, note and notification modes. TTS and notification
runtimes now delegate to the shared service, note mode is used to distill a
selected excerpt into a short project note. Expose the new endpoint via
/api/text/summarize and route it through the common request middleware.

Client voice/summarize.ts accepts a mode option and points at the new
endpoint with an absolute URL that respects the desktop server origin.
VS Code webview swaps the stubbed tts summarize path for /api/text/summarize
and hardens URL parsing with window.location.href as the base.

packages/web/server/lib/notifications/DOCUMENTATION.md

@@ -67,7 +67,7 @@ This module provides notification message preparation utilities for the web serv
   - `broadcastUiNotification(payload)`
 
 ### Template runtime API (template-runtime.js)
-- `createNotificationTemplateRuntime(dependencies)`: creates shared notification/template + zen helper runtime.
+- `createNotificationTemplateRuntime(dependencies)`: creates shared notification/template runtime and consumes shared text summarization from `packages/web/server/lib/text/summarization.js` in `notification` mode.
 - Returned API:
   - `resolveNotificationTemplate(template, variables)`
   - `shouldApplyResolvedTemplateMessage(template, resolved, variables)`