refactor: simplify project nav to AI Chat (overview) + Design only

- AI Chat nav item now routes to /overview instead of /v_ai_chat
- Removed Plan, Docs, Tech, Journey nav items
- Deleted old v_ai_chat page
- Cleaned up unused imports and route detection logic

Made-with: Cursor

components/layout/left-rail.tsx

@@ -2,26 +2,12 @@
 
 import { cn } from "@/lib/utils";
 import {
-  LayoutGrid,
-  Inbox,
-  Users,
-  Receipt,
-  Globe,
-  FileText,
-  MessageCircle,
   Settings,
   HelpCircle,
   User,
-  DollarSign,
   Key,
   Palette,
-  Target,
-  Megaphone,
-  ClipboardList,
-  Code2,
   Sparkles,
-  Cog,
-  GitBranch,
 } from "lucide-react";
 import { Button } from "@/components/ui/button";
 import { Separator } from "@/components/ui/separator";
@@ -31,11 +17,8 @@ import { toast } from "sonner";
 type NavSection = "home" | "ai-chat" | "docs" | "plan" | "design" | "tech" | "journey" | "settings";
 
 const NAV_ITEMS = [
-  { id: "plan" as NavSection, icon: ClipboardList, label: "Plan", href: "/project/{projectId}/plan" },
-  { id: "docs" as NavSection, icon: FileText, label: "Docs", href: "/project/{projectId}/docs" },
+  { id: "home" as NavSection, icon: Sparkles, label: "AI Chat", href: "/project/{projectId}/overview" },
   { id: "design" as NavSection, icon: Palette, label: "Design", href: "/project/{projectId}/design" },
-  { id: "tech" as NavSection, icon: Cog, label: "Tech", href: "/project/{projectId}/tech" },
-  { id: "journey" as NavSection, icon: GitBranch, label: "Journey", href: "/project/{projectId}/journey" },
 ];
 
 interface LeftRailProps {
@@ -61,27 +44,6 @@ export function LeftRail({ activeSection, onSectionChange, projectName, projectI
       <div className="w-full flex flex-col items-center">
       {/* Main Navigation Items */}
       <div className="flex flex-col gap-2 w-full items-center">
-        {/* AI Chat - Always visible */}
-        {projectName && projectId && (
-          <Link
-            href={`/${workspace}/project/${projectId}/v_ai_chat`}
-            className={cn(
-              "flex flex-col items-center gap-1 w-full py-2 px-2 transition-all relative",
-              activeSection === "ai-chat"
-                ? "text-primary bg-primary/5"
-                : "text-muted-foreground hover:text-foreground hover:bg-accent"
-            )}
-            title="AI Chat"
-          >
-            <Sparkles className="h-5 w-5" />
-            <span className="text-[10px] font-medium">AI Chat</span>
-            {activeSection === "ai-chat" && (
-              <div className="absolute left-0 top-1/2 -translate-y-1/2 h-10 w-1 bg-primary" />
-            )}
-          </Link>
-        )}
-
-        {/* Other Nav Items */}
         {NAV_ITEMS.map((item) => {
           if (!projectId) return null;
           const fullHref = `/${workspace}${item.href.replace('{projectId}', projectId)}`;