feat(website): add samples/cookbook page with recipe browser

Integrates the cookbook/ folder into the website's Samples page:

Data Structure:
- Add cookbook/cookbook.yml manifest defining cookbooks and recipes
- Add .schemas/cookbook.schema.json for validation
- Add COOKBOOK_DIR constant to eng/constants.mjs

Build Integration:
- Add generateSamplesData() to generate samples.json from cookbook.yml
- Include recipe variants with file paths for each language
- Add samples count to manifest.json

Website UI:
- Create samples.ts with FuzzySearch, language/tag filtering
- Replace placeholder samples.astro with functional recipe browser
- Recipe cards with language indicators and action buttons
- Language tabs for switching between implementations
- View Recipe/View Example buttons open modal
- GitHub link for each recipe

Features:
- Search recipes by name/description
- Filter by programming language (Node.js, Python, .NET, Go)
- Filter by tags (multi-select with Choices.js)
- 5 recipes across 4 languages = 20 recipe variants

website/public/data/manifest.json

@@ -1,12 +1,13 @@
 {
-  "generated": "2026-02-02T02:45:34.292Z",
+  "generated": "2026-02-02T04:05:33.889Z",
   "counts": {
-    "agents": 140,
-    "prompts": 134,
-    "instructions": 163,
-    "skills": 28,
+    "agents": 145,
+    "prompts": 138,
+    "instructions": 167,
+    "skills": 32,
     "collections": 39,
     "tools": 6,
-    "total": 504
+    "samples": 5,
+    "total": 521
   }
 }