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/collections.json

@@ -78,6 +78,11 @@
           "path": "instructions/copilot-sdk-python.instructions.md",
           "kind": "instruction",
           "usage": null
+        },
+        {
+          "path": "skills/copilot-sdk/SKILL.md",
+          "kind": "skill",
+          "usage": null
         }
       ],
       "path": "collections/copilot-sdk.collection.yml",