fix: remove @supabase/ssr entirely to fix MIDDLEWARE_INVOCATION_FAILED

@supabase/ssr uses __dirname internally which crashes in Vercel's Edge
runtime, causing MIDDLEWARE_INVOCATION_FAILED even without a middleware
file. Replaced with @supabase/supabase-js directly:
- Server client: manual cookie-based session restoration
- Browser client: direct createClient from supabase-js
- Admin client: already using supabase-js

https://claude.ai/code/session_01H2aRGDaKgarPvhay2HxN6Y

lib/supabase/client.ts

@@ -1,9 +1,9 @@
-import { createBrowserClient } from "@supabase/ssr";
+import { createClient as createSupabaseClient } from "@supabase/supabase-js";
 import type { Database } from "@/types/database.types";
 
 // Client Supabase côté navigateur (composants client)
 export const createClient = () =>
-  createBrowserClient<Database>(
+  createSupabaseClient<Database>(
     process.env.NEXT_PUBLIC_SUPABASE_URL!,
     process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!
   );