feat(editor): add note linking and backlinks

[rui-typelets]

Summary

Adds bi-directional note linking with [[note]] syntax and backlinks panel to the editor.

Problem

Users couldn't connect notes together to build a knowledge graph. Unlike tools like Obsidian or Roam, there was no way to:

• Link from one note to another
• See which notes reference the current note
• Navigate between connected notes

Solution

Note Linking

• [[ trigger - Type [[ to open note search popup
• NoteLink TipTap extension - Custom node for rendering styled note links
• NoteLinkSuggestion extension - Handles [[ trigger with unique plugin key to avoid conflicts with slash commands
• Full note search - Shows all notes (not just filtered view) excluding current, deleted, hidden, and archived
• Click navigation - Clicking a note link navigates to that note

Backlinks Panel

• Incoming links - "X notes link here" section showing notes that reference current note
• Outgoing links - Shows notes the current note links to
• Collapsible sections - Expand/collapse each section independently
• Quick navigation - Click any backlink to jump to that note

UI Integration

• Toolbar dropdown - Links menu with "External Link" and "Link to Note" options
• Slash command - /Link to Note inserts [[ to trigger search
• Styled chips - Note links display as blue chips with 📝 icon

Technical Details

• NoteLink.ts: TipTap Node extension with data-type="noteLink" and data-note-id attributes
• NoteLinkSuggestion.ts: Extension with custom PluginKey to coexist with SlashCommands
• noteLinkUtils.ts: Separated helper function to satisfy ESLint fast-refresh rule
• useBacklinks.ts: Parses HTML content to extract note IDs via regex, computes incoming/outgoing links
• BacklinksPanel.tsx: Collapsible panel with navigation buttons
• useNotes.ts: Added allNotes export for unfiltered note access
• layout.ts: Extended EditorProps with notes and onSelectNote

Testing

• Type [[ triggers note search popup
• Search filters notes as you type
• Selecting note inserts styled link
• Clicking link navigates to note
• Backlinks panel shows incoming links
• Outgoing links section shows links in current note
• Works across folders (not limited to current view)
• Toolbar dropdown works
• Slash command /Link to Note works
• Lint and type-check pass

[github-actions]

🎉 This PR is included in version 1.40.0 🎉

The release is available on GitHub release

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