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/store.go

@@ -150,6 +150,12 @@ CREATE TABLE IF NOT EXISTS deploy_logs (
 	created_at TEXT NOT NULL DEFAULT (datetime('now'))
 );
 
+CREATE TABLE IF NOT EXISTS poll_states (
+	stage_id    TEXT PRIMARY KEY REFERENCES stages(id) ON DELETE CASCADE,
+	last_tag    TEXT NOT NULL DEFAULT '',
+	last_polled TEXT NOT NULL DEFAULT (datetime('now'))
+);
+
 -- Seed the settings row if it does not exist.
 INSERT OR IGNORE INTO settings (id) VALUES (1);
 `