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/mcp/McpDropdown.tsx

@@ -127,7 +127,7 @@ export const McpDropdown: React.FC<McpDropdownProps> = ({ headerIconButtonClass
         return (
           <div
             key={serverName}
-            className="flex items-center justify-between gap-2 px-2 py-1.5 rounded-lg hover:bg-muted/50"
+            className="flex items-center justify-between gap-2 px-2 py-1.5 rounded-lg hover:bg-interactive-hover/50"
           >
             <div className="min-w-0 flex-1">
               <div className="flex items-center gap-2 min-w-0">
@@ -235,7 +235,7 @@ export const McpDropdown: React.FC<McpDropdownProps> = ({ headerIconButtonClass
               <div className="flex items-center gap-1">
                 <button
                   type="button"
-                  className="p-1 rounded-md text-muted-foreground hover:text-foreground hover:bg-muted transition-colors"
+                  className="p-1 rounded-md text-muted-foreground hover:text-foreground hover:bg-interactive-hover transition-colors"
                   disabled={isSpinning}
                   onClick={handleRefresh}
                   aria-label="Refresh"
@@ -281,7 +281,7 @@ export const McpDropdown: React.FC<McpDropdownProps> = ({ headerIconButtonClass
           <span className="typography-ui-label font-semibold">MCP Servers</span>
           <button
             type="button"
-            className="p-1 rounded-md text-muted-foreground hover:text-foreground hover:bg-muted transition-colors"
+            className="p-1 rounded-md text-muted-foreground hover:text-foreground hover:bg-interactive-hover transition-colors"
             disabled={isSpinning}
             onClick={handleRefresh}
             aria-label="Refresh"