Feat v0.4.0 notes surface (#22)

Add Notes as a standard installable surface package (type: full,
tier: starlark). Markdown editor with sidebar note list, live
preview toggle, auto-save, pin/archive, and full-text search.
Zero kernel changes — proves extension stack E2E.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/notes/README.md

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+# Notes
+
+Markdown notes surface with sidebar navigation, live preview, and search.
+
+## Status: v0.1.0
+
+Core CRUD with markdown textarea and inline preview.
+
+## Features
+
+- Create, edit, archive notes
+- Markdown editing with live preview toggle
+- Auto-save with debounce (1s)
+- Pin important notes to top
+- Full-text search across title and body
+- Light/dark theme support
+
+## Planned
+
+- v0.4.1: Folders + navigation tree
+- v0.4.2: Tags + enhanced search
+- v0.4.3: Backlinks + `[[wikilinks]]`
+- v0.4.4: Rich editor (CodeMirror 6) + import/export
+
+## Data
+
+Single `notes` table in ext_data:
+
+| Column | Type | Description |
+|--------|------|-------------|
+| title | text | Note title |
+| body | text | Markdown content |
+| folder_id | text | Folder reference (v0.4.1) |
+| pinned | int | 0 or 1 |
+| archived | int | Soft delete flag |
+
+## API
+
+| Method | Path | Description |
+|--------|------|-------------|
+| GET | /notes | List notes (lightweight, no body) |
+| POST | /notes | Create note |
+| GET | /notes/:id | Get note with full body |
+| PUT | /notes/:id | Update note |
+| DELETE | /notes/:id | Archive (or hard delete with ?hard=1) |
+| GET | /search?q=term | Search title and body |
+| GET | /stats | Note counts |
+
+## Keyboard Shortcuts
+
+- `Ctrl/Cmd+S` — Force save
+- `Tab` — Insert two spaces