feat: HLS streaming, transcripts, agent course generation & landing-page course previews (#663)

New features:
- HLS video encoding/streaming (hls routes, hls-encoder) and a media
  transcripts pipeline (transcripts route + media-transcript queries)
- AI assistant chat vs. run model: agent-course-generation worker/queue,
  run-monitor pane, chat-changes card, content ask-ai bar
- Per-theme course-page previews across org landing-page themes (bold,
  classic, corporate, editorial, etc.) with a shared course token/component set
- View-as-student mode and login-link / link-invite invite flows

Refactor:
- Extract packages/core consolidating config (env, storage, dashboard-url),
  services and utils previously duplicated under apps/api/src/config
- Remove legacy agent service modules (chat-tools, chat-context,
  context-window, document, fetch-url, lesson-content)
- Relax Cross-Origin-Resource-Policy to allow cross-origin media embedding
- Add format script to tenant-router so turbo run format covers it

packages/utils/src/functions/index.ts

@@ -2,3 +2,4 @@ export * from './array';
 export * from './fileValidation';
 export * from './sanitize';
 export * from './slug';
+export * from './transcript-vtt';

packages/utils/src/functions/transcript-vtt.ts

@@ -0,0 +1,45 @@
+export interface TranscriptVttSegment {
+  start: number;
+  end: number;
+  text: string;
+}
+
+function formatVttTime(seconds: number): string {
+  if (!Number.isFinite(seconds) || seconds < 0) {
+    seconds = 0;
+  }
+
+  const totalMs = Math.round(seconds * 1000);
+  const hours = Math.floor(totalMs / 3_600_000);
+  const minutes = Math.floor((totalMs % 3_600_000) / 60_000);
+  const secs = Math.floor((totalMs % 60_000) / 1000);
+  const ms = totalMs % 1000;
+
+  const pad = (n: number, width: number) => n.toString().padStart(width, '0');
+
+  return `${pad(hours, 2)}:${pad(minutes, 2)}:${pad(secs, 2)}.${pad(ms, 3)}`;
+}
+
+/**
+ * Build a minimal WEBVTT caption file from transcript segment timestamps.
+ */
+export function segmentsToWebVtt(segments: TranscriptVttSegment[]): string {
+  const lines = ['WEBVTT', ''];
+
+  let cueIndex = 1;
+  for (const segment of segments) {
+    const text = segment.text.trim();
+    if (!text) continue;
+
+    const start = formatVttTime(segment.start);
+    const end = formatVttTime(Math.max(segment.end, segment.start + 0.001));
+
+    lines.push(String(cueIndex));
+    lines.push(`${start} --> ${end}`);
+    lines.push(text);
+    lines.push('');
+    cueIndex++;
+  }
+
+  return lines.join('\n');
+}