feat(01-03): add Edge middleware + internal validate-token API route

- src/middleware.ts: Edge-compatible token validation via fetch() (no Drizzle import)
- src/app/api/internal/validate-token/route.ts: Node.js route queries clients.token via Drizzle
- Invalid tokens rewrite to /not-found (404); matcher scoped to /c/:path*

src/middleware.ts

@@ -0,0 +1,35 @@
+import { NextRequest, NextResponse } from 'next/server';
+
+export async function middleware(request: NextRequest) {
+  const pathname = request.nextUrl.pathname;
+
+  // Extract token from path: /c/[token]/...
+  const tokenMatch = pathname.match(/^\/c\/([a-zA-Z0-9_-]+)/);
+  if (!tokenMatch) {
+    return NextResponse.rewrite(new URL('/not-found', request.url));
+  }
+
+  const token = tokenMatch[1];
+
+  try {
+    // Call internal Node.js API route — Edge middleware cannot use postgres-js directly
+    // postgres-js requires Node.js net/tls which are unavailable in the Edge runtime
+    const validateUrl = new URL(
+      `/api/internal/validate-token?token=${encodeURIComponent(token)}`,
+      request.url
+    );
+    const res = await fetch(validateUrl.toString());
+
+    if (!res.ok) {
+      return NextResponse.rewrite(new URL('/not-found', request.url));
+    }
+
+    return NextResponse.next();
+  } catch {
+    return NextResponse.rewrite(new URL('/not-found', request.url));
+  }
+}
+
+export const config = {
+  matcher: ['/c/:path*'],
+};