Migrate backend from PocketBase to Directus

Full cutover: auth, users, collection and friendships now run on Directus
via @directus/sdk, with owner/visibility rules enforced by Directus
permissions.

- middleware: Directus session (directus_auth cookie) with token refresh
- /login is Directus (email normalized to lowercase), new /register page
  (first/last name, username) backed by public registration
- collection, friends and profile pages + all API endpoints ported;
  ownership and addressee-only accept/decline enforced by permissions
- display names use first_name/last_name everywhere (nav, friends, profile)
- PocketBase SDK, POCKETBASE_URL and pb_schema.json removed
- README and compose updated for DIRECTUS_URL

docker-compose.yml

@@ -6,8 +6,8 @@ services:
         build: .
         restart: unless-stopped
         environment:
-            # Full URL of the PocketBase instance to use (required).
-            POCKETBASE_URL: ${POCKETBASE_URL:-https://pokeshare.namarusaja.me}
+            # Full URL of the Directus instance to use (required).
+            DIRECTUS_URL: ${DIRECTUS_URL:-https://directus.namarusaja.me}
         healthcheck:
             # / redirects to /login (302) — check a 200 endpoint instead
             test: "wget -q -O /dev/null http://localhost:4321/login || exit 1"