fix: refine desktop sidebar and prompt anchor (#212)

## Related Issue

Related to #210

## Problem

The desktop sidebar uses a full update card, the prompt anchor can stay
expanded after navigation, and fixed macOS header spacing can overlap
native window controls. The sidebar also carries obsolete banner assets.

## What changed

- Replaced the sidebar update card with the supplied green update button
between the banner and collapse control
- Added hover and keyboard-focus release notes while keeping the
existing update dialog for download and restart controls
- Redesigned the prompt anchor as compact lines with synchronized hover
previews, exact prompt navigation, and immediate collapse after
selection or pointer exit
- Derived collapsed macOS header spacing from Electron's native
title-bar safe area
- Updated sidebar banner assets, user documentation, changesets, tests,
and the committed web bundle

## Verification

- `pnpm --filter @pymodel/pythinker-web exec vitest run` — 1,002 tests
passed
- `pnpm exec vitest run apps/desktop/tests/window-appearance.spec.ts` —
4 tests passed
- `pnpm lint` — 0 errors
- `pnpm typecheck`
- `npm run build` in `docs/`
- `node apps/pythinker-code/scripts/check-web-assets.mjs`
- Electron development build reviewed with available-update and
prompt-anchor states

## Checklist

- [x] I have read the
[CONTRIBUTING](https://github.com/PyModel/pythinker-code/blob/main/CONTRIBUTING.md)
document.
- [x] I have linked a related issue (external PRs: the issue must have a
maintainer's `/approve`).
- [x] I have added tests that prove my feature works.
- [x] Ran `gen-changesets` skill, or this PR needs no changeset.
- [x] Ran `gen-docs` skill, or this PR needs no doc update.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Conversation navigation now shows compact prompt markers with hover or
focus previews of prompts and responses.
* Available desktop updates appear as a sidebar button with release
notes and update controls.
* macOS desktop window controls and sidebar spacing adapt more
accurately to the title bar.

* **Bug Fixes**
* Improved update-button accessibility, positioning, and release-notes
behavior.
  * Added support for additional Python syntax keywords.

* **Documentation**
* Updated desktop update guidance to reflect the new sidebar experience.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: elkaix

.changeset/compact-prompt-anchor.md

@@ -2,4 +2,4 @@
 "@pymodel/pythinker-code": patch
 ---
 
-Make the chat prompt anchor a compact line index that expands to prompt labels.
+Make the chat prompt anchor a compact line index that opens prompt and response previews.

.changeset/show-desktop-update-card.md

@@ -2,4 +2,4 @@
 "@pymodel/pythinker-code": patch
 ---
 
-Show available desktop updates in a sidebar card with compact download progress.
+Show available desktop updates as a sidebar button with release notes and update controls.

apps/desktop/src/window-options.ts

@@ -5,6 +5,7 @@ export function windowAppearanceOptions(platform: NodeJS.Platform): BrowserWindo
     return {
       autoHideMenuBar: true,
       titleBarStyle: 'hiddenInset',
+      titleBarOverlay: true,
       trafficLightPosition: { x: 16, y: 16 },
       // A transparent NSWindow is non-opaque with a clear background, which
       // removes native corners and shadow. Vibrancy does not require it.

apps/desktop/tests/window-appearance.spec.ts

@@ -11,6 +11,7 @@ describe('desktop window appearance configuration', () => {
 
     expect('frame' in opts).toBe(false)
     expect(opts['titleBarStyle']).toBe('hiddenInset')
+    expect(opts['titleBarOverlay']).toBe(true)
     expect(opts['trafficLightPosition']).toEqual({ x: 16, y: 16 })
     // Native corners and shadow require an opaque window.
     expect('transparent' in opts).toBe(false)

apps/pythinker-code/dist-web/.web-bundle-manifest.json

@@ -1,4 +1,4 @@
 {
-  "sourceHash": "f88e4160eddd99fef98d31820eb0a5e660fc8209a97edb99e62b445d7f9b7365",
-  "sourceFileCount": 403
+  "sourceHash": "ad0be8811299a96afcfa243941b6812309cf4597345759fac292edbcf7dea1e4",
+  "sourceFileCount": 404
 }