fix(memory): bound visualizer PCM cache and feed episode cache

The visualizer's PCM cache decoded the entire episode into RAM (22050 Hz
mono s16 ~160 MB/hr of audio) and held it until stop() — a 3-hour episode
pinned ~500 MB and long-form content hit 2.5 GB. The 4x decode also pulled
the whole remote file even when only minutes were listened to.

- audio-pcm-cache: sliding window around the playback position — the
  decode head caps at maxAheadSec (600s) ahead of the cursor, segments
  older than keepBehindSec (300s) are pruned, and the tail refills as
  playback advances. Steady state ~40 MB regardless of episode length;
  a backward seek past the window restarts a segment there (the existing
  seek-hole mechanism, no new failure mode).
- feed: cap the full-parse episode cache at 1000 episodes/feed so
  archive-heavy subscriptions can't pin their entire history in RAM;
  the visible list stays bounded by the user's cache preference and
  fetch-more keeps working within the ceiling.
- tests: pin the new head-cap and prune contracts (8/8 in
  audio-pcm-cache.test.ts; full suite 193 pass).

Also includes the in-flight cleanup/refactor pass (cover-art resolve
helper, page and comment tightening, ESLint config removal).

src/api/rss-parser.ts

@@ -100,24 +100,20 @@ export const parseRSSItem = (item: string, feedUrl: string, index: number): Epis
   const epDescription = cleanField(getTagValue(item, "description"))
   const pubDate = new Date(getTagValue(item, "pubDate") || Date.now())
 
-  // Audio URL + file size + MIME type from <enclosure>
   const enclosure = item.match(/<enclosure[^>]*url=["']([^"']+)["'][^>]*>/i)
   const audioUrl = enclosure?.[1] ?? ""
   const fileSizeStr = getAttr(item, "enclosure", "length")
   const fileSize = fileSizeStr ? parseInt(fileSizeStr, 10) : undefined
   const mimeType = getAttr(item, "enclosure", "type") || undefined
 
-  // Duration from <itunes:duration>
   const durationRaw = getTagValue(item, "itunes:duration")
   const duration = parseDuration(durationRaw)
 
-  // Episode & season numbers
   const episodeNumRaw = getTagValue(item, "itunes:episode")
   const episodeNumber = episodeNumRaw ? parseInt(episodeNumRaw, 10) : undefined
   const seasonNumRaw = getTagValue(item, "itunes:season")
   const seasonNumber = seasonNumRaw ? parseInt(seasonNumRaw, 10) : undefined
 
-  // Episode type & explicit
   const episodeType = parseEpisodeType(getTagValue(item, "itunes:episodeType"))
   const explicitRaw = getTagValue(item, "itunes:explicit").toLowerCase()
   const explicit = explicitRaw === "yes" || explicitRaw === "true" ? true : undefined
@@ -135,7 +131,6 @@ export const parseRSSItem = (item: string, feedUrl: string, index: number): Epis
     pubDate,
   }
 
-  // Only set optional fields if present
   if (episodeNumber !== undefined && !isNaN(episodeNumber)) ep.episodeNumber = episodeNumber
   if (seasonNumber !== undefined && !isNaN(seasonNumber)) ep.seasonNumber = seasonNumber
   if (episodeType) ep.episodeType = episodeType