feat(profiles): implement AI profile management system

Add new profiles view component with sidebar integration and state management for AI provider profiles. Users can now create and manage custom AI profiles for different tasks (e.g., heavy-task with Claude Opus, debugging with Codex).

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

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

app/src/components/layout/sidebar.tsx

@@ -21,6 +21,7 @@ import {
   GripVertical,
   Trash2,
   Undo2,
+  UserCircle,
 } from "lucide-react";
 import {
   DropdownMenu,
@@ -357,6 +358,11 @@ export function Sidebar() {
           icon: Wrench,
           shortcut: NAV_SHORTCUTS.tools,
         },
+        {
+          id: "profiles",
+          label: "AI Profiles",
+          icon: UserCircle,
+        },
       ],
     },
   ];