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/chat/ChatContainer.tsx

@@ -298,13 +298,13 @@ export const ChatContainer: React.FC = () => {
             <div className="relative bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/80 z-10">
                 {showScrollButton && sessionMessages.length > 0 && (
                     <div className="absolute bottom-full left-1/2 -translate-x-1/2 mb-2">
-                            <Button
-                                variant="outline"
-                                size="sm"
-                                onClick={() => scrollToBottom({ force: true })}
-                                className="rounded-full h-8 w-8 p-0 shadow-none bg-background/95 hover:bg-accent"
-                                aria-label="Scroll to bottom"
-                            >
+                                <Button
+                                  variant="outline"
+                                  size="sm"
+                                  onClick={() => scrollToBottom({ force: true })}
+                                  className="rounded-full h-8 w-8 p-0 shadow-none bg-background/95 hover:bg-interactive-hover"
+                                  aria-label="Scroll to bottom"
+                                >
 
                             <RiArrowDownLine className="h-4 w-4" />
                         </Button>