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

apps/tenant-router/package.json

@@ -7,11 +7,16 @@
     "dev": "wrangler dev",
     "deploy": "wrangler deploy",
     "tail": "wrangler tail",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "format": "prettier --write ."
   },
   "devDependencies": {
     "@cloudflare/workers-types": "^4.20250109.0",
+    "@types/pg": "^8.16.0",
     "typescript": "^5.5.2",
     "wrangler": "4.21.x"
+  },
+  "dependencies": {
+    "pg": "^8.18.0"
   }
 }