Assign readable ticket keys from project code and sequence.

Replace UUID-looking sync labels in TUI and web with keys like TAS-1,
while keeping the remote UUID for task-master matching.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/sqlite/db.go

@@ -44,6 +44,10 @@ func Open(path string, secret []byte) (*DB, error) {
 		_ = sqlDB.Close()
 		return nil, err
 	}
+	if err := db.backfillTicketKeys(); err != nil {
+		_ = sqlDB.Close()
+		return nil, err
+	}
 	return db, nil
 }