chore: update Astro/Preact deps and add TS/ESLint tooling

- Bump @astrojs/* and preact to latest minor versions
- Add Astro TS plugin and language server packages
- Introduce ESLint plugins for React, Astro, and TypeScript
- Update TypeScript to 5.9.x
- Enable @astrojs/ts-plugin in tsconfig.json
- Regenerate package-lock.json accordingly

tsconfig.json

@@ -12,5 +12,8 @@
     "jsxImportSource": "preact",
     "strictNullChecks": true,
     "allowJs": true
-  }
-}
+  },
+  "plugins": [
+    { "name": "@astrojs/ts-plugin" }
+  ]
+}