test(podcasts): integration suite + RLS auditor + contract widening (task 1.10)

cmd/server/tests/podcast_test.go — six suites, the shared-dev-DB
doctrine (test*-named libraries, cascading cleanup, no binary
fixtures):

- TestPodcastRLSSurfaces: THE AUDITOR (invariant 13) — non-subscriber
  404 on feed detail + SSR page (existence leak), episodes absent from
  generic media reads, admin escape, subscriber visibility, then the
  hidden-library flip hiding an already-subscribed feed (the feed
  policy's library-visibility join). Seeding runs as the FIRST ADMIN —
  the seed identity has neither subscription nor users row, so podcast
  INSERT..RETURNING (SELECT policy under FORCE) 42501s for it;
  production pods run as exactly that admin (invariant 12). All direct
  row probes read through the admin scope for the same reason.
- TestPodcastAddFeedFlow: member add + subscribe + metadata-only
  upsert; duplicate-URL dedupe (no second row); allow_member_feeds
  gate (member 403 / admin 201 / subscribe-still-allowed).
- TestPodcastShrunkenFeedRetention: feed purges an episode from the
  XML, both rows persist (upsert-without-delete pin, D14).
- TestPodcastEditSegregation: generic edit 400 + write-to-file refusal
  for episodes; control book edit unaffected.
- TestPodcastDownloadWorker (ffmpeg-generated tone at runtime): file
  lands at <download-root>/<feed-slug>/NNNN-…, audio_metadata probed;
  re-download of a downloaded episode never re-fetches (idempotency
  pin, enclosure-hit counted); dead enclosure → failed + persisted
  reason + metadata intact. Fetch/SSRF tests swap the client via
  SetPodcastHTTPClientForTests (the production client refuses
  loopback httptest servers by design — the real client gets its own
  negative test in services).
- TestPodcastScannerExclusion: SetFolders on a podcasts library root
  yields zero scanner folders (invariant 4 pin) — MediaScanner
  .FolderCount() accessor added.

Unit: internal/services/podcast_rss_test.go — namespace-aware parsing
fixture (three XML namespaces, fallback chains, hosts/guests),
duration spellings, RFC-822 variants, explicit variants, slug/path
layout, enclosure-extension selection, stripHTML, and the SSRF matrix
(private/loopback/link-local/multicast/mapped-v6 blocked; a loopback
httptest server PROVES the production client refuses it).

suites green: full integration run 161s / 0 failures; vitest 12 files
163 tests.

Contract widening: TestContractPin_MediaListBothBranches' raw-row
allowlist gains the 15 podcast episode columns (additive; documented in
docs/contract_pins.md — inert defaults on scan rows). Bruno: bruno/
podcasts/ mirrors the §8 endpoints (12 requests) + Bookhoard env vars.
tests/ui/COVERAGE.md rows 18-23: podcasts pages/lifecycle/RLS/chain —
Playwright sweep pending.

internal/services/podcast_service.go

@@ -129,6 +129,12 @@ type AddFeedResult struct {
 	FetchError string
 }
 
+// FeedError returns the fetch failure text ("" when the fetch was fine
+// or there is no feed row).
+func (r *AddFeedResult) FeedError() string {
+	return r.FetchError
+}
+
 // AddFeed implements POST /api/podcasts/feeds (plan §8): fetch+parse the
 // user-supplied URL, create-or-reuse the feed row, upsert metadata-only
 // episodes, subscribe the creator. Authorization on explicit arguments