feat(podcasts): chain playback + Continue section — sequence mode in the web player (phase 2 core)

D7 chain-by-default, delivered with minimal player surgery:

- ReaderMetadata gains PodcastSequence: the neighboring DOWNLOADED
  episodes in the caller's effective order (D5 override applied,
  feed-native fallback; computed in the reader route for
  source='podcast_episode' items — RLS already scoped the reads; gaps
  never enter the chain, invariant 6). ?single=1 escapes chaining (the
  'play single episode' affordance).
- Audio reader renders the sequence into body[data-json]
  (AudioReaderConfigJSON — books produce the identical shape minus the
  sequence key, so the reader path is unchanged for them) and an
  'Ep N/M' indicator + prev/next episode controls in the header.
- audio.ts: the last-track 'ended' handler chains into the next
  episode's reader page (final progress push precedes navigation);
  back button exits episodes to their feed page. Books are untouched —
  no sequence context, zero behavior change. Day-one chaining is
  page-navigation based (progress persists; position restores).

Continue aggregation (2.5): GetPodcastContinueForUser (in-progress
episodes, most-recent-first, ≥95% excluded) feeds a Continue section
on /podcasts — sorted most recently listened, cards show 'Ep N · title'
— ahead of All Feeds. Cards prefer the continue line over the
description.

internal/database/queries.sql.go

@@ -9310,6 +9310,62 @@ func (q *Queries) GetPanelData(ctx context.Context, arg GetPanelDataParams) (Pan
 	return i, err
 }
 
+const GetPodcastContinueForUser = `-- name: GetPodcastContinueForUser :many
+SELECT mi.source_feed_id,
+       mi.id,
+       mi.title,
+       mi.feed_position,
+       rp.percentage,
+       rp.last_read_at
+FROM reading_progress rp
+JOIN media_items mi ON mi.id = rp.media_item_id
+WHERE rp.user_id = $1
+  AND mi.source = 'podcast_episode'
+  AND rp.percentage > 0
+  AND rp.percentage < 0.995
+ORDER BY rp.last_read_at DESC
+`
+
+type GetPodcastContinueForUserRow struct {
+	SourceFeedID pgtype.UUID        `db:"source_feed_id" json:"source_feed_id"`
+	ID           pgtype.UUID        `db:"id" json:"id"`
+	Title        string             `db:"title" json:"title"`
+	FeedPosition pgtype.Int4        `db:"feed_position" json:"feed_position"`
+	Percentage   pgtype.Float8      `db:"percentage" json:"percentage"`
+	LastReadAt   pgtype.Timestamptz `db:"last_read_at" json:"last_read_at"`
+}
+
+// Continue aggregation (plan 2.5): the caller's IN-PROGRESS episodes
+// (0 < pct < finishedThreshold) across ALL subscribed feeds, most
+// recent first. Go groups per feed — the first row per feed IS the
+// continue target.
+func (q *Queries) GetPodcastContinueForUser(ctx context.Context, userID pgtype.UUID) ([]GetPodcastContinueForUserRow, error) {
+	rows, err := q.db.Query(ctx, GetPodcastContinueForUser, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	items := []GetPodcastContinueForUserRow{}
+	for rows.Next() {
+		var i GetPodcastContinueForUserRow
+		if err := rows.Scan(
+			&i.SourceFeedID,
+			&i.ID,
+			&i.Title,
+			&i.FeedPosition,
+			&i.Percentage,
+			&i.LastReadAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
 const GetPodcastEpisode = `-- name: GetPodcastEpisode :one
 SELECT id, library_id, title, subtitle, author, isbn, description, file_path, file_size, mime_type, cover_image_path, series, series_number, tags, narrators, authors, authors_search, publishers, publishers_search, abridged, explicit, asin, date_published, publisher, contributors, language, edition, page_count, genre, copyright_year, goodreads_id, openlibrary_id, google_books_id, added_by_admin_id, created_at, imported_at, updated_at, format_group, format_mimetype, is_reflowable, has_fixed_layout, total_characters, chapter_count, entitlement_id, revision_number, kobo_content_id, kobo_metadata, manga_type, reading_direction, series_count, volume, imprint, age_rating, web_url, story_arc, is_black_and_white, metadata_notes, community_rating, alternate_info, scan_information, summary, metadata_overrides, missing_scan_count, archived_at, chapter_metadata, library_type_name, audio_metadata, tags_search, contributors_search, narrators_search, file_sha256, opf_identifier, opf_uuid, hash_confidence, source, source_feed_id, episode_guid, feed_position, season_number, episode_number, enclosure_url, declared_duration_seconds, transcript_url, chapters_url, hosts, guests, download_state, download_error, download_attempts FROM media_items
 WHERE id = $1 AND source = 'podcast_episode'