Feat v0.4.6 sidebar restructure

Restructure the notes sidebar with a two-tab header (Notes / Outline)
and relocate the document outline from the editor-side panel into the
sidebar's Outline tab with active heading tracking.

- Add SidebarTabs component with Notes/Outline tabs; Outline disabled
  when no note is selected
- Add SidebarOutline component with nested heading hierarchy
  (H1→H2→H3), depth indentation, and click-to-scroll
- Add RAF-throttled scroll listener for active heading highlighting
  based on scroll position (preview getBoundingClientRect / CM6 viewport)
- Lift headings, scrollToHeading, and activeHeadingIdx state to NotesApp
  via EditorPane callback props
- Remove old DocumentOutline component and .doc-outline CSS
- Auto-reset to Notes tab when active note is deleted
- Bump notes package to v0.7.0

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

ROADMAP.md

@@ -301,12 +301,12 @@ Zero platform special-casing. Proves the full extension stack E2E.
 | View mode setting | ✅ | `editor_mode` in manifest settings + localStorage persistence. Toolbar cycles rendered → edit → split. |
 | Document outline | ✅ | `parseHeadings()` extracts headings (skips code blocks). Collapsible `DocumentOutline` panel with click-to-scroll (CM6 line dispatch or preview `scrollIntoView`). Debounced 300ms updates. |
 
-### v0.4.6 — Sidebar Restructure (planned)
+### v0.4.6 — Sidebar Restructure (complete)
 
 | Step | Status | Description |
 |------|--------|-------------|
-| Sidebar tabs | | Two-tab header at top of sidebar: "Notes" (folders → tags → search → list) and "Outline" (heading tree for active note). Outline tab enabled only when a note is selected. |
-| Heading tree | | Nested heading hierarchy (H1 → H2 → H3) with depth indentation. Click → scroll to heading in editor/preview. Current heading highlighted based on scroll position. |
+| Sidebar tabs | ✅ | Two-tab header at top of sidebar: "Notes" (folders → tags → search → list) and "Outline" (heading tree for active note). Outline tab enabled only when a note is selected. |
+| Heading tree | ✅ | Nested heading hierarchy (H1 → H2 → H3) with depth indentation. Click → scroll to heading in editor/preview. Current heading highlighted based on scroll position. |
 
 ### v0.4.7 — Note Graph (planned)