feat(content): serve the mounted content folder under /content (spec 003)

Audio with range requests, library.json, Homer books; LRC parser. Content
stays out of git and the image.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/shared/lrc.ts

@@ -0,0 +1,20 @@
+export interface LrcLine {
+  time: number;
+  text: string;
+}
+
+const STAMP = /\[(\d+):(\d{1,2}(?:\.\d+)?)\]/g;
+
+/** Parses LRC timed lyrics: metadata tags and untimed lines are skipped, output is sorted by time. */
+export function parseLrc(text: string): LrcLine[] {
+  const lines: LrcLine[] = [];
+  for (const raw of text.split(/\r?\n/)) {
+    const stamps = [...raw.matchAll(STAMP)];
+    if (stamps.length === 0) continue;
+    const lyric = raw.replace(STAMP, "").trim();
+    for (const [, min, sec] of stamps) {
+      lines.push({ time: Math.round((Number(min) * 60 + Number(sec)) * 1000) / 1000, text: lyric });
+    }
+  }
+  return lines.sort((a, b) => a.time - b.time);
+}