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/theme.ts

@@ -1,28 +1,13 @@
 /**
- * Theme CSS Variable Manager
- * Handles dynamic theme switching by updating CSS custom properties
+ * Terminal Theme Resolver
+ * Resolves the active theme (built-in, custom, or system-derived) to colors.
  */
 
 import type { TerminalColors } from "@opentui/core";
 import type { ThemeJson } from "../types/theme-schema";
-import { THEME_JSON } from "../constants/themes";
-import { getCustomThemes } from "./custom-themes";
 import { resolveTheme as resolveThemeJson } from "./theme-resolver";
 import { generateSystemTheme } from "./system-theme";
 
-/**
- * Apply CSS variable data-theme attribute
- */
-export function setThemeAttribute(themeName: string) {
-  if (typeof document === "undefined") return;
-  const root = document.documentElement;
-  root.setAttribute("data-theme", themeName);
-}
-
-export async function loadThemes() {
-  return await getCustomThemes();
-}
-
 export function resolveTerminalTheme(
   themes: Record<string, ThemeJson>,
   name: string,
@@ -32,9 +17,5 @@ export function resolveTerminalTheme(
   if (name === "system" && system) {
     return resolveThemeJson(generateSystemTheme(system, mode), mode);
   }
-  const theme = themes[name] ?? themes.catppuccin;
-  if (!theme) {
-    return resolveThemeJson(THEME_JSON.catppuccin, mode);
-  }
-  return resolveThemeJson(theme, mode);
+  return resolveThemeJson(themes[name] ?? themes.catppuccin, mode);
 }