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/text/DOCUMENTATION.md

@@ -0,0 +1,35 @@
+# Text Module Documentation
+
+## Purpose
+This module provides shared text transformation helpers that are not owned by a single product surface. Today it contains the shared summarization pipeline used by TTS, notifications, and note distillation flows.
+
+## Entrypoints and structure
+- `packages/web/server/lib/text/summarization.js`: Shared summarize + sanitize helpers backed by opencode.ai zen API.
+
+## Public exports
+
+### Summarization (summarization.js)
+- `summarizeText({ text, threshold, maxLength, zenModel, mode })`: Shared summarization entrypoint.
+- `sanitizeForTTS(text)`: Sanitizes text for speech output.
+- `sanitizeForNotification(text)`: Sanitizes text for compact notification output.
+- `sanitizeForNote(text)`: Sanitizes text for short note/distillation output.
+
+## Modes
+- `tts`: Speakable summary for TTS flows.
+- `notification`: Short plain-text summary for notification bodies.
+- `note`: Distilled short project-memory note.
+
+## Response contract
+
+### `summarizeText`
+Returns object with:
+- `summary`: Final transformed text.
+- `summarized`: Boolean indicating whether model summarization succeeded.
+- `reason`: Optional failure/skip reason.
+- `originalLength`: Optional original text length.
+- `summaryLength`: Optional final summary length.
+
+## Notes for contributors
+- Keep this module neutral. Do not re-couple it to TTS-specific naming or routing.
+- Add new mode semantics here when multiple product surfaces need the same text pipeline.
+- Prefer mode-specific prompt and sanitize behavior over creating duplicated summarizers in unrelated modules.