feat(docker-watcher): phase 5 - registry client & poller

Gitea registry client with tag listing and pattern matching, cron-based
polling scheduler with first-poll safety, poll state persistence.
DeployTriggerer interface for decoupled deploy triggering.

internal/store/poll_state.go

@@ -0,0 +1,75 @@
+package store
+
+import (
+	"database/sql"
+	"errors"
+	"fmt"
+)
+
+// PollState tracks the last polled tag for a stage, enabling the poller to
+// detect new tags since the previous poll cycle.
+type PollState struct {
+	StageID    string `json:"stage_id"`
+	LastTag    string `json:"last_tag"`
+	LastPolled string `json:"last_polled"`
+}
+
+// GetPollState returns the poll state for a given stage.
+func (s *Store) GetPollState(stageID string) (PollState, error) {
+	var ps PollState
+	err := s.db.QueryRow(
+		`SELECT stage_id, last_tag, last_polled FROM poll_states WHERE stage_id = ?`,
+		stageID,
+	).Scan(&ps.StageID, &ps.LastTag, &ps.LastPolled)
+	if errors.Is(err, sql.ErrNoRows) {
+		return PollState{}, fmt.Errorf("poll state for stage %s: %w", stageID, ErrNotFound)
+	}
+	if err != nil {
+		return PollState{}, fmt.Errorf("query poll state: %w", err)
+	}
+	return ps, nil
+}
+
+// UpsertPollState inserts or updates the poll state for a stage.
+func (s *Store) UpsertPollState(ps PollState) error {
+	_, err := s.db.Exec(
+		`INSERT INTO poll_states (stage_id, last_tag, last_polled)
+		 VALUES (?, ?, ?)
+		 ON CONFLICT(stage_id) DO UPDATE SET last_tag=excluded.last_tag, last_polled=excluded.last_polled`,
+		ps.StageID, ps.LastTag, ps.LastPolled,
+	)
+	if err != nil {
+		return fmt.Errorf("upsert poll state: %w", err)
+	}
+	return nil
+}
+
+// DeletePollState removes the poll state for a stage.
+func (s *Store) DeletePollState(stageID string) error {
+	_, err := s.db.Exec(`DELETE FROM poll_states WHERE stage_id = ?`, stageID)
+	if err != nil {
+		return fmt.Errorf("delete poll state: %w", err)
+	}
+	return nil
+}
+
+// GetAllPollStates returns all poll states, ordered by last_polled descending.
+func (s *Store) GetAllPollStates() ([]PollState, error) {
+	rows, err := s.db.Query(
+		`SELECT stage_id, last_tag, last_polled FROM poll_states ORDER BY last_polled DESC`,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("query poll states: %w", err)
+	}
+	defer rows.Close()
+
+	var states []PollState
+	for rows.Next() {
+		var ps PollState
+		if err := rows.Scan(&ps.StageID, &ps.LastTag, &ps.LastPolled); err != nil {
+			return nil, fmt.Errorf("scan poll state: %w", err)
+		}
+		states = append(states, ps)
+	}
+	return states, rows.Err()
+}