feat: add optional mood to thoughts with custom moods support

Mood is an optional label+emoji string (e.g. "relaxed 😌") on thoughts.
Users can define up to 8 custom moods in profile settings.
Mood federates via AP Note JSON and displays on thought cards.

crates/adapters/postgres-search/src/tests.rs

@@ -27,6 +27,7 @@ async fn seed_thought(pool: &sqlx::PgPool, username: &str, content: &str) -> (Us
         visibility: Visibility::Public,
         content_warning: None,
         sensitive: false,
+        mood: None,
     });
     trepo.save(&t).await.unwrap();
     (u, t)