feat(podcasts): feed poller + podcast_poll_interval_seconds setting (task 1.6)

One ticker re-reading its interval from the settings registry each
cycle (live tunable — the cache stays honest because writes go through
the settings API path, AGENTS.md gotcha #2). Per tick: list feeds
(first-admin identity, invariant 12), skip is_complete feeds (back
off; explicit refresh still works), poll each (conditional GET via
stored validators), and apply the subscriber auto-download policy
union after each successful fetch so new episodes queue without
waiting a tick.

Schema/registry: podcast_poll_interval_seconds (default 3600s, floor
300s, category podcasts) — seeded with ON CONFLICT DO NOTHING per the
idempotency rule.

internal/database/queries/queries.sql

@@ -4943,7 +4943,7 @@ WHERE source_feed_id = $1
 -- source filter keeps scan items out of podcast search.
 SELECT * FROM media_items
 WHERE source = 'podcast_episode'
-  AND ($1 = '' OR title ILIKE '%' || $1 || '%' OR description ILIKE '%' || $1 || '%')
+  AND (sqlc.arg('search_query')::text = '' OR title ILIKE '%' || sqlc.arg('search_query')::text || '%' OR description ILIKE '%' || sqlc.arg('search_query')::text || '%')
 ORDER BY feed_position ASC NULLS LAST, date_published ASC NULLS LAST
 LIMIT 50;
 
@@ -4957,9 +4957,43 @@ SELECT f.*,
        s.created_at AS subscribed_at
 FROM podcast_subscriptions s
 JOIN podcast_feeds f ON f.id = s.feed_id
-WHERE s.user_id = $1
-  AND ($2 = '' OR f.title ILIKE '%' || $2 || '%'
-       OR COALESCE(s.display_name, '') ILIKE '%' || $2 || '%'
-       OR COALESCE(f.host, '') ILIKE '%' || $2 || '%'
-       OR COALESCE(f.publisher, '') ILIKE '%' || $2 || '%')
+WHERE s.user_id = sqlc.arg('user_id')
+  AND (sqlc.arg('search_query')::text = '' OR f.title ILIKE '%' || sqlc.arg('search_query')::text || '%'
+       OR COALESCE(s.display_name, '') ILIKE '%' || sqlc.arg('search_query')::text || '%'
+       OR COALESCE(f.host, '') ILIKE '%' || sqlc.arg('search_query')::text || '%'
+       OR COALESCE(f.publisher, '') ILIKE '%' || sqlc.arg('search_query')::text || '%')
 ORDER BY COALESCE(s.display_name, f.title) ASC;
+
+-- name: GetNextQueuedEpisode :one
+-- Sequential download worker's claim source (single worker, day one).
+SELECT * FROM media_items
+WHERE source = 'podcast_episode' AND download_state = 'queued'
+ORDER BY updated_at ASC
+LIMIT 1;
+
+-- name: CountQueuedEpisodes :one
+SELECT COUNT(*) FROM media_items
+WHERE source = 'podcast_episode' AND download_state IN ('queued', 'downloading');
+
+-- name: CountPodcastEpisodesForFeed :one
+SELECT COUNT(*) FROM media_items
+WHERE source_feed_id = $1 AND source = 'podcast_episode';
+
+-- ============================================================================
+-- GENERIC reader_settings KV (podcast order override, plan D5: key
+-- podcast_order:<feed_id>). The pre-existing reader_settings queries are
+-- hard-keyed to 'reader_settings'; these two are the generic form.
+-- ============================================================================
+
+-- name: GetUserSettingByKey :one
+SELECT setting_value FROM reader_settings
+WHERE user_id = $1 AND setting_key = $2;
+
+-- name: UpsertUserSettingByKey :exec
+INSERT INTO reader_settings (user_id, setting_key, setting_value)
+VALUES ($1, $2, $3)
+ON CONFLICT (user_id, setting_key)
+DO UPDATE SET setting_value = EXCLUDED.setting_value, updated_at = NOW();
+
+-- name: DeleteUserSettingByKey :exec
+DELETE FROM reader_settings WHERE user_id = $1 AND setting_key = $2;