fix(alarms): give up after three runs without delivery (FLAW-12)

New column alarm_failures counts ticker runs in which no channel
delivered; at three the alarm is marked as done and a warning is logged
instead of retrying every minute forever. Success, a new due date or
reopening the task starts over with three attempts.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/storage/sqlite.go

@@ -375,6 +375,7 @@ func (s *Store) migrate() error {
 
 	// Idempotent column migrations for existing databases
 	columnMigrations := []string{
+		"ALTER TABLE thoughts ADD COLUMN alarm_failures INTEGER NOT NULL DEFAULT 0;",
 		"ALTER TABLE documents ADD COLUMN archived_at TEXT NOT NULL DEFAULT '';",
 		"ALTER TABLE documents ADD COLUMN archived_by TEXT NOT NULL DEFAULT '';",
 		"ALTER TABLE users ADD COLUMN username TEXT NOT NULL DEFAULT '';",