docs(website): add Notion case study and improve onboarding

The Electron guide currently uses a teaching fixture. Add a real Notion clipboard case with REA findings, short source excerpts and responsive figures, alongside the existing DX-Ball reconstruction.

- Trace the saved Notion 7.6.1 preload API through its wrappers to the clipboard receiver. Attribute the separate web-cache module probes to their original harness. Public content uses relative source locations and generic example data; packages and complete captures stay local.
- Add a Showcases index and links from the homepage and JavaScript guide. Simplify homepage copy while preserving the approved headline and closing question.
- Show copyable agent installation prompts and the direct setup command. Keep terminal cursors blinking consistently and respect reduced-motion settings.
- Provide one Notes example ZIP. Generate it from the six public source files before website checks and manual Pages deployment; verify its contents against the source. Pages remains manual-only.

Validation:
- `npm run check:fast`
- `python3 scripts/prepare-website.py` and `python3 scripts/verify-website.py`
- Browser checks at `/` and `/rea/`: downloads, prompt/command copying, responsive layouts, keyboard navigation, reduced motion and DX-Ball comparison controls.
- Published REA 4.1.0 preload analysis and feature traces; source/claim/privacy review.
- Real Hopper/Ghidra verification: not performed (website-only change).

.github/workflows/website-check.yml

@@ -6,6 +6,7 @@ on:
     paths:
       - "website/**"
       - "scripts/verify-website.py"
+      - "scripts/prepare-website.py"
       - ".github/workflows/**"
   workflow_dispatch:
 
@@ -24,5 +25,7 @@ jobs:
     steps:
       - name: Check out the repository
         uses: actions/checkout@v4
+      - name: Prepare the example download
+        run: python3 scripts/prepare-website.py
       - name: Check website links and publishing configuration
         run: python3 scripts/verify-website.py

.github/workflows/website-pages.yml

@@ -21,6 +21,8 @@ jobs:
     steps:
       - name: Check out the repository
         uses: actions/checkout@v4
+      - name: Prepare the example download
+        run: python3 scripts/prepare-website.py
       - name: Check website links and publishing configuration
         run: python3 scripts/verify-website.py
       - name: Configure Pages