feat(podcasts): API endpoints — add/list/detail, subscriptions, downloads, sequence, search (task 1.7)

The §8 surface, wired through main.go → router.Config →
/api/podcasts (JWT). Scoping is the engine's (D20): lookups outside the
caller's scope simply return no rows → 404; the only Go-level checks
are explicit-argument authorization (AddFeed's library +
allow_member_feeds gate) and the admin role on feed deletion.

Endpoints: POST/GET /feeds (add: fetch+parse+upsert+subscribe, optional
download_all; list: subscriptions + episode counts + facet values
computed in Go — feed counts are tens), GET /feeds/:id (detail with
download states + gap count), PUT/DELETE /subscription (the ONLY
user-writable podcast state, D9; unsubscribe retains files per D6),
POST /refresh, POST /episodes/:eid/download (+ episode_ids[] bulk and
eid='all' = Download All, exactly the non-downloaded set),
PUT /order (D5 per-user override in the reader_settings KV —
podcast_order:<feed_id>; 'native' deletes the row so default and
explicit choice are indistinguishable), GET /sequence (effective order
— override applied, native fallback — DOWNLOADED-only with the gap
list; this payload powers web chain mode and, per §15, the future
media3 queue), GET /search (subscription-scoped feed + episode search
covering un-downloaded and historical rows, D14), DELETE /feeds/:id
(admin; best-effort file removal, cascade deletes rows).

Gap definition (countGaps): an un-downloaded episode with a downloaded
episode AFTER it in list order — the D8 'middle episodes missing'
banner condition.

cmd/server/main.go

@@ -177,6 +177,12 @@ func main() {
 	matchingHandler := handlers.NewMatchingHandler(queries, connManager)
 	jobsHandler := handlers.NewJobsHandler(queries, worker)
 
+	// Podcast subsystem: fetcher service + sequential download worker +
+	// poller. One instance trio per server (per-feed locks dedupe).
+	podcastService := services.NewPodcastService(queries)
+	podcastWorker := services.NewPodcastDownloadWorker(queries, podcastService)
+	podcastHandler := handlers.NewPodcastHandler(queries, podcastService, podcastWorker)
+
 	e := echo.New()
 
 	// Set up validator
@@ -237,6 +243,9 @@ func main() {
 		CollectionHandler:       collectionHandler,
 		FiltersHandler:          filtersHandler,
 		DashboardHandler:        dashboardHandler,
+		PodcastHandler:          podcastHandler,
+		PodcastService:          podcastService,
+		PodcastWorker:           podcastWorker,
 		DashboardService:        dashboardService,
 		SeriesHandler:           seriesHandler,
 		OPDSHandler:             opdsHandler,