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

packages/ui/src/components/sections/skills/SkillsSidebar.tsx

@@ -294,7 +294,7 @@ export const SkillsSidebar: React.FC<SkillsSidebarProps> = ({ onItemSelect }) =>
             <Button
               variant="ghost"
               onClick={() => setRenameDialogSkill(null)}
-              className="text-foreground hover:bg-muted hover:text-foreground"
+              className="text-foreground hover:bg-interactive-hover hover:text-foreground"
             >
               Cancel
             </Button>
@@ -329,7 +329,7 @@ const SkillListItem: React.FC<SkillListItemProps> = ({
     <div
       className={cn(
         'group relative flex items-center rounded-md px-1.5 py-1 transition-all duration-200',
-        isSelected ? 'dark:bg-accent/80 bg-primary/12' : 'hover:dark:bg-accent/40 hover:bg-primary/6'
+        isSelected ? 'bg-interactive-selection' : 'hover:bg-interactive-hover'
       )}
     >
       <div className="flex min-w-0 flex-1 items-center">