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/stores/progress.ts

@@ -64,16 +64,10 @@ function createProgressStore() {
 		 */
 		whenReady: () => progressInit,
 
-		/**
-		 * Get progress for a specific episode.
-		 */
 		get(episodeId: string): Progress | undefined {
 			return progressMap()[episodeId];
 		},
 
-		/**
-		 * Get all progress entries.
-		 */
 		all(): Record<string, Progress> {
 			return progressMap();
 		},
@@ -102,18 +96,12 @@ function createProgressStore() {
 			persist();
 		},
 
-		/**
-		 * Check if an episode is completed.
-		 */
 		isCompleted(episodeId: string): boolean {
 			const p = progressMap()[episodeId];
 			if (!p || p.duration <= 0) return false;
 			return p.position / p.duration >= COMPLETION_THRESHOLD;
 		},
 
-		/**
-		 * Get progress percentage (0-100) for an episode.
-		 */
 		getPercent(episodeId: string): number {
 			const p = progressMap()[episodeId];
 			if (!p || p.duration <= 0) return 0;
@@ -151,9 +139,6 @@ function createProgressStore() {
 			persist();
 		},
 
-		/**
-		 * Clear all progress data.
-		 */
 		clear(): void {
 			setProgressMap({});
 			persist();