feat: discoverability (NodeInfo, hashtags) and moderation (domain/actor blocking)

- NodeInfo at /.well-known/nodeinfo + /nodeinfo/2.0
- Hashtags #MoviesDiary + #MovieTitle on review posts; /tags/{tag} redirect
- Domain blocking: blocked_domains table, admin API + HTML, inbox enforcement
- Per-actor blocking: blocked_actors table, user API + HTML, BlockActivity send/receive
- Delivery filter excludes blocked actors and blocked-domain inboxes

crates/adapters/sqlite/migrations/0013_blocked_actors.sql

@@ -0,0 +1,6 @@
+CREATE TABLE blocked_actors (
+    local_user_id    TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+    remote_actor_url TEXT NOT NULL,
+    blocked_at       TEXT NOT NULL,
+    PRIMARY KEY (local_user_id, remote_actor_url)
+);