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>

CHANGELOG.md

@@ -2,6 +2,36 @@
 
 All notable changes to Switchboard Core are documented here.
 
+## v0.4.6 — Sidebar Restructure
+
+### Added
+
+- **Sidebar tabs**: Two-tab header ("Notes" / "Outline") replaces the static
+  sidebar header. Notes tab contains folder tree, tag filter, search, and note
+  list. Outline tab shows the document heading tree for the active note.
+  Outline tab disabled (grayed) when no note is selected.
+- **Sidebar outline**: Document outline relocated from editor-side panel into
+  the sidebar's Outline tab. Nested heading hierarchy (H1→H2→H3) with depth
+  indentation via `padding-left`. Click heading scrolls to it in both preview
+  and CM6 editor modes.
+- **Active heading tracking**: Scroll listener (RAF-throttled) highlights the
+  current heading in the sidebar outline based on scroll position. Uses
+  `getBoundingClientRect()` in preview/split mode and CM6 viewport line in
+  edit mode.
+
+### Changed
+
+- Notes package version bumped from 0.6.0 to 0.7.0.
+- `EditorPane` exposes headings, scroll function, and active heading index to
+  parent via callback props (`onHeadingsChange`, `scrollToHeadingRef`,
+  `onActiveHeadingChange`).
+- Sidebar auto-resets to Notes tab when active note is deleted.
+
+### Removed
+
+- Old `DocumentOutline` component and `.doc-outline` CSS styles (replaced by
+  sidebar outline).
+
 ## v0.4.5 — Editor Modes + Document Outline
 
 ### Added