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/providers/ProvidersPage.tsx

@@ -542,7 +542,7 @@ export const ProvidersPage: React.FC = () => {
                   type="button"
                   className={cn(
                     "flex w-fit items-center justify-between gap-2 rounded-lg border border-input bg-transparent px-3 py-2 typography-ui-label",
-                    "hover:bg-muted focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
+                    "hover:bg-interactive-hover focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring"
                   )}
                 >
                   <span className={candidateProviderId ? "text-foreground" : "text-muted-foreground"}>

packages/ui/src/components/sections/providers/ProvidersSidebar.tsx

@@ -77,7 +77,7 @@ export const ProvidersSidebar: React.FC<ProvidersSidebarProps> = ({ onItemSelect
                 key={provider.id}
                 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'
                 )}
               >
                 <button