refactor(website): convert to ES modules with TypeScript

- Replace all inline scripts with TypeScript modules
- Create page-specific modules for agents, prompts, instructions, skills, collections, index
- Create core modules: utils.ts, search.ts, modal.ts, choices.ts, jszip.ts, theme.ts
- Remove window global exports, use proper ES module imports
- Add type interfaces for all data structures
- Use data-base-path attribute on body for base URL handling
- Bundle Choices.js and JSZip via npm instead of CDN
- Astro pages now just have single script import each

website/data/manifest.json

@@ -1,5 +1,5 @@
 {
-  "generated": "2026-01-28T03:53:29.513Z",
+  "generated": "2026-01-28T04:53:00.935Z",
   "counts": {
     "agents": 140,
     "prompts": 134,