Add Zod validation layer and AI blog generation

Introduce a schema-first validation layer and an AI blog generation
feature, plus one-command Cloudflare provisioning.

- src/schemas/ holds Zod input schemas for post, content, case,
  settings, AI, and keywords; parseForm() in src/lib/form.ts validates
  FormData and returns per-field errors.
- Migrate all admin POST handlers to parseForm, showing field-level
  errors and only redirecting once validation passes.
- Add blog_keywords table and posts.focus_keyword (migration 0002);
  uniqueSlug() centralised in src/data/content.ts.
- Add src/lib/ai.ts (OpenAI-compatible chat completions + optional
  Tavily research) and /admin/ai for AI settings, keyword queue, and
  draft generation.
- Add scripts/setup.mjs (npm run setup) to provision D1/KV, set
  secrets, and optionally migrate, seed, and deploy.
- Document AI secrets, Workers Builds deploy flow, and new schemas
  across README and AGENTS docs.

package-lock.json

@@ -19,7 +19,8 @@
         "lucide-react": "^1.44.0",
         "marked": "^18.0.12",
         "react": "^19.3.0",
-        "react-dom": "^19.3.0"
+        "react-dom": "^19.3.0",
+        "zod": "^4.6.2"
       },
       "devDependencies": {
         "@types/node": "^22.20.2",
@@ -9455,9 +9456,9 @@
       }
     },
     "node_modules/zod": {
-      "version": "4.6.1",
-      "resolved": "https://registry.npmjs.org/zod/-/zod-4.6.1.tgz",
-      "integrity": "sha512-341aRWQsve0rvronKNTqZpjmzdbUDlFuzHaI/XLg/Ej82qffDJRRfBTCuv7+9q/rMjB6LSLyEBnW4InJeMtt/Q==",
+      "version": "4.6.2",
+      "resolved": "https://registry.npmjs.org/zod/-/zod-4.6.2.tgz",
+      "integrity": "sha512-lh5RCAGFa1Cm2hjtNwLQhSs/AsqdWnTQaBER9fEwN/88pSh7KOtJavtBx/0VlkN/uFd61SwYmljLMDAsHlvzBQ==",
       "license": "MIT",
       "funding": {
         "url": "https://github.com/sponsors/colinhacks"