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/ChatMessage.tsx

@@ -898,7 +898,7 @@ const ChatMessage: React.FC<ChatMessageProps> = ({
                         displayParts.length === 0 ? null : (
                         <FadeInOnReveal>
                             <div className="flex justify-end">
-                                <div className="max-w-[85%] rounded-2xl rounded-br-sm bg-primary/10 dark:bg-primary/10 px-5 py-3 shadow-sm border border-primary/5">
+                                <div style={{ backgroundColor: 'var(--chat-user-message-bg)' }} className="max-w-[85%] rounded-2xl rounded-br-sm px-5 py-3 shadow-sm border border-primary/5">
                                     <MessageBody
                                         messageId={message.info.id}
                                         parts={displayParts}
@@ -932,7 +932,7 @@ const ChatMessage: React.FC<ChatMessageProps> = ({
                         </FadeInOnReveal>
                         )
                     ) : (
-                        <div className="relative pl-4 ml-1">
+                        <div className="relative">
                             {shouldShowHeader && (
                                 <MessageHeader
                                     isUser={isUser}