Add EmDash CMS blog + hero standardization + seed fix

- Add EmDash CMS integration with SQLite and local storage
- Add blog collection (seed/seed.json) with 3 sample posts
- Add /บทความ list page and /บทความ/[slug] detail page
- Add blog section to homepage
- Fix reserved field slugs (slug, published_at removed from fields)
- Fix date field mapping (publishedAt camelCase)
- Fix featured image URL for admin-uploaded images (meta.storageKey)
- Standardize all product page hero sections
- Update navigation with 'บทความ' link
- Configure Google OAuth provider

.gitignore

@@ -8,3 +8,20 @@ dist/
 .DS_Store
 *.swp
 *.swo
+
+# Database
+*.db
+*.db-shm
+*.db-wal
+*.bak
+*.old
+*.test-run
+
+# Agent context
+.context/
+
+# Uploaded media
+uploads/
+
+# Generated
+emdash-env.d.ts