feat: introduced a token-based theming system across the UI

* feat: added themes system

* feat: smart sidebar auto-hide for files/diff tabs + lower files sidebar threshold

* feat: added Checkbox component and update theming

- Add reusable Checkbox component for toggles across UI
- Replace several inputs with Checkbox in settings and commands panels
- Add DiffIcon and apply surface/border theming to key UI areas

* feat: Add convert-vscode-theme.cjs to convert VS Code themes to OpenChamber format

* refactor: remove unused permission logic from ChatInput

- Remove unused permission rules parsing logic from ChatInput
- Memoize renderTheme in DiffWorkerProvider to avoid unnecessary recalculations
- Remove forceOpaque helper in vscode theme adapter

* fix: guard VSCode theme loading in MarkdownRenderer

* feat: add custom user themes loading and reload

- Load user themes from ~/.config/openchamber/themes at runtime
- Expose /api/config/themes to fetch custom themes
- Allow theme reloading from Settings → Theme → Reload themes in the UI

AGENTS.md

@@ -72,6 +72,17 @@ All scripts are in `package.json`.
 - No new deps unless asked.
 - Never add secrets (`.env`, keys) or log sensitive data.
 
+## Theme System (MANDATORY for UI work)
+
+When working on any UI components, styling, or visual changes, agents **MUST** study the theme system skill first.
+
+**Before starting any UI work:**
+```
+skill({ name: "theme-system" })
+```
+
+This skill contains all color tokens, semantic logic, decision tree, and usage patterns. All UI colors must use theme tokens - never hardcoded values or Tailwind color classes.
+
 ## Recent changes
 - Releases + high-level changes: `CHANGELOG.md`
 - Recent commits: `git log --oneline` (latest tags: `v1.4.6`, `v1.4.5`)