Feedback inbox: read/unread + delete

Make the admin Feedback section a real inbox.

* DB: feedback.read_at column (schema + idempotent migration).
* API: feedback list returns read_at; POST /api/admin/feedback/{id}/read
  {read} toggles it; DELETE /api/admin/feedback/{id} removes a message
  (both admin-gated). admin_stats gains feedback_unread; the Attention strip
  and the tab badge now count UNREAD, not total.
* Frontend: unread messages are highlighted with an accent rail + dot; an
  Unread filter joins the category chips; each message has Mark read/unread
  and Delete (confirm), with optimistic updates that revert on failure.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

goodnews/db.py

@@ -236,7 +236,8 @@ CREATE TABLE IF NOT EXISTS feedback (
     user_id INTEGER REFERENCES users(id) ON DELETE SET NULL,
     visitor_hash TEXT NOT NULL DEFAULT '',
     day TEXT NOT NULL,
-    created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP
+    created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    read_at TEXT
 );
 CREATE INDEX IF NOT EXISTS idx_feedback_created ON feedback(created_at);
 """
@@ -304,3 +305,8 @@ def _migrate(conn: sqlite3.Connection) -> None:
     for column, decl in health_columns.items():
         if column not in source_cols:
             conn.execute(f"ALTER TABLE sources ADD COLUMN {column} {decl}")
+
+    # feedback.read_at (admin inbox read/unread) added later.
+    fb_cols = {row["name"] for row in conn.execute("PRAGMA table_info(feedback)")}
+    if fb_cols and "read_at" not in fb_cols:
+        conn.execute("ALTER TABLE feedback ADD COLUMN read_at TEXT")