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/ui/README.md

@@ -25,6 +25,22 @@ packages/ui/
 └── jsrepo.json        # jsrepo configuration
 ```
 
+## Storybook
+
+We maintain a Storybook instance at `packages/storybook` to make it easy to browse, visualize, and reuse every UI component in the app. Instead of digging through source code or guessing how a component looks, you can see each piece rendered in isolation with its variants, props, and states documented.
+
+This is especially useful when you're building a new feature and need to find the right existing component — check Storybook first before creating something from scratch.
+
+<img alt="Storybook Preview" src="https://brand.cdn.clsrio.com/storybook-preview.png" />
+
+To run it locally:
+
+```bash
+cd packages/storybook && pnpm dev
+```
+
+See `packages/storybook/README.md` for detailed instructions on creating stories and publishing.
+
 ## Content Structure
 
 ### Base Components (`src/base/`)