feat(ui): add per-project themes and fix scrolling/styling issues

- Add per-project theme support with theme selector in sidebar
- Fix file diffs scrolling in agent output modal with proper overflow handling
- Improve cursor styling across all interactive elements (buttons, tabs, checkboxes)
- Enhance hotkey styling to use consistent theme colors
- Fix Kanban board flash/refresh issues with React.memo optimizations
- Update tab component for better theme integration with proper active states

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

app/src/components/views/kanban-column.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import { memo } from "react";
 import { useDroppable } from "@dnd-kit/core";
 import { cn } from "@/lib/utils";
 import type { ReactNode } from "react";
@@ -13,7 +14,7 @@ interface KanbanColumnProps {
   headerAction?: ReactNode;
 }
 
-export function KanbanColumn({
+export const KanbanColumn = memo(function KanbanColumn({
   id,
   title,
   color,
@@ -48,4 +49,4 @@ export function KanbanColumn({
       </div>
     </div>
   );
-}
+});