Add ct-code-editor backlinks

[bfollington]

• Break out Chat recipe
• Re-use common chatbot.tsx
• Format pass
• ct-code-editor backlink support

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Summary by cubic

Adds [[backlink]] autocomplete and Cmd/Ctrl+click navigation to ct-code-editor, and centralizes chat into a reusable Chat recipe. Also adds a Note pattern that supports backlinks and simple edit/read tools.

• New Features

  • ct-code-editor: [[...]] autocomplete from a mentionable Charm list, backlink highlighting, and backlink-click event on Cmd/Ctrl+click.
  • New Note pattern: Markdown editor with backlinks (uses ct-code-editor) and tools editNote/readNote; optional Chat tab.
  • Shared Chat recipe: Unified chat UI with model select, prompt input, tool wiring, and clear/cancel controls; used by Tools and Outliner patterns.

• Migration

  • Props: chat renamed to messages in patterns; pass tools into Chat({ messages, tools }).
  • ct-code-editor: provide $mentionable={allCharms} for backlink suggestions; handle onbacklink-click to navigate.
  • Outliner and Tools now render Chat via the shared recipe; Outliner adds an expandChat toggle.