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/db/src/queries/media-transcript/media-transcript.ts

@@ -54,6 +54,38 @@ export async function upsertMediaTranscript(
   }
 }
 
+/**
+ * Update only the editable content (segments + derived text) of an asset's
+ * transcript. Scoped by asset + organization. Returns the updated row or
+ * `null` when no transcript exists for the asset.
+ */
+export async function updateMediaTranscriptContent(
+  assetId: string,
+  organizationId: string,
+  patch: { segments: TMediaTranscript['segments']; text: string },
+  dbClient: DbOrTxClient = db
+): Promise<TMediaTranscript | null> {
+  try {
+    const now = new Date().toISOString();
+    const [row] = await dbClient
+      .update(schema.mediaTranscript)
+      .set({
+        segments: patch.segments,
+        text: patch.text,
+        updatedAt: now
+      })
+      .where(
+        and(eq(schema.mediaTranscript.assetId, assetId), eq(schema.mediaTranscript.organizationId, organizationId))
+      )
+      .returning();
+
+    return row ?? null;
+  } catch (error) {
+    console.error('updateMediaTranscriptContent error:', error);
+    throw new Error('Failed to update media transcript content');
+  }
+}
+
 export async function getMediaTranscriptByAsset(
   assetId: string,
   organizationId: string,