delete messages + fix layout overflow

- DELETE /api/channels/{id}/messages/{msg_id} — soft delete, own only
- Broadcasts WsEvent::Delete to subscribers
- UI: "Del" button on hover for own messages (turns red)
- Fix layout: h-full + overflow-hidden on flex containers
- ScrollArea gets min-h-0 to properly constrain in flex
- Messages no longer push compose past viewport

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/colony/src/routes.rs

@@ -278,6 +278,47 @@ pub async fn post_message(
     Ok((StatusCode::CREATED, Json(message)))
 }
 
+pub async fn delete_message(
+    State(state): State<AppState>,
+    Path((channel_id, msg_id)): Path<(String, String)>,
+    Query(user_param): Query<UserParam>,
+) -> Result<impl IntoResponse> {
+    let user_id = resolve_user(&state.db, &user_param).await?;
+
+    // Verify message exists and belongs to this user
+    let row = sqlx::query_as::<_, MessageWithUserRow>(
+        "SELECT m.*, u.id as u_id, u.username, u.display_name, u.role, u.created_at as u_created_at \
+         FROM messages m JOIN users u ON m.user_id = u.id WHERE m.id = ? AND m.channel_id = ?",
+    )
+    .bind(&msg_id)
+    .bind(&channel_id)
+    .fetch_optional(&state.db)
+    .await?;
+
+    let row = match row {
+        Some(r) => r,
+        None => return Err(AppError::NotFound("Message not found".into())),
+    };
+
+    if row.user_id != user_id {
+        return Err(AppError::BadRequest("Can only delete your own messages".into()));
+    }
+
+    // Soft delete
+    sqlx::query("UPDATE messages SET deleted_at = strftime('%Y-%m-%dT%H:%M:%SZ', 'now') WHERE id = ?")
+        .bind(&msg_id)
+        .execute(&state.db)
+        .await?;
+
+    // Broadcast delete event
+    let tx = state.get_sender(&channel_id).await;
+    let _ = tx.send(WsEvent::Delete {
+        id: uuid::Uuid::parse_str(&msg_id).unwrap(),
+    });
+
+    Ok(StatusCode::NO_CONTENT)
+}
+
 // ── Joined row type for message + user ──
 
 #[derive(Debug, sqlx::FromRow)]