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/utils/feeds-persistence.ts

@@ -134,7 +134,6 @@ export function saveFeedsToFile(feeds: Feed[], windowDays?: number): void {
 		}
 	})().catch(() => {});
 }
-/** Load sources from config.json */
 export async function loadSourcesFromFile<T>(): Promise<T[] | null> {
 	try {
 		const cfg = await loadConfig();
@@ -144,7 +143,6 @@ export async function loadSourcesFromFile<T>(): Promise<T[] | null> {
 		return null;
 	}
 }
-/** Save sources to config.json */
 export function saveSourcesToFile<T>(sources: T[]): void {
 	updateConfig({ sources: sources as unknown as PodcastSource[] });
 }