feat(changelog): one source file per release, generated outputs

Release notes now live in changelog/<version>.md (front matter with
version and date, then ## App and ## VS Code sections grouped into
New, Improvements, Fixes, Misc) plus changelog/unreleased.md for what
has not shipped. `bun run changelog:build` renders CHANGELOG.md,
packages/vscode/CHANGELOG.md, and changelog/index.json from them;
`changelog:check` fails when the outputs are behind and runs in CI and
in release:prepare. `oc-dev create-release` promotes unreleased.md to
the versioned file dated today and rebuilds.

The existing history was split mechanically: every bullet kept, sorted
into groups by keyword, five hand-typed headers with one-digit days
normalised to YYYY-MM-DD (the update dialog matched none of them). The
generated files keep today's release headers, which the update dialog,
the release workflow, and the website match by regex.

Claude-Session: https://claude.ai/code/session_01VqV56Hez25hTxXH4ipJfzH

changelog/1.6.1.md

@@ -0,0 +1,33 @@
+---
+version: 1.6.1
+date: 2026-01-30
+---
+
+## App
+
+### New
+- UI: update dialog now includes the changelog.
+- Terminal: added optional on-screen key bar (Esc/Ctrl/arrows/Enter) for easier terminal navigation.
+- Notifications: added "Notify for subtasks" toggle to silence child-session notifications during multi-run (thanks to @Jovines).
+- Worktrees: starting new worktree sessions now defaults to HEAD when no start point is provided.
+- Git: commit message generation now includes untracked files and handles `git diff --no-index` comparisons reliably (thanks to @MrLYC).
+
+### Improvements
+- Mobile: revamped chat controls on small screens with a unified controls drawer (thanks to @nelsonPires5).
+- Reliability: improved event-stream reconnection when the app becomes visible again.
+- Desktop: improved macOS window chrome and header spacing, including steady traffic lights on older macOS versions (thanks to @yulia-ivashko).
+
+### Fixes
+- Chat: added Stop button to cancel generation mid-response.
+
+## VS Code
+
+### New
+- Chat: added Apply Patch tool support for opening files in editor.
+
+### Improvements
+- Chat: improved compact controls on narrow panels with a unified drawer for model and tool options.
+- Reliability: improved event stream reconnection when the panel is hidden/shown or VS Code regains focus.
+
+### Fixes
+- Chat: added Stop button to cancel generation mid-response.