refactor: move blog from EmDash to Astro content collections

EmDash CMS integration is being removed. The blog content is
moved to native Astro content collections (markdown files in
src/content/blog/) which works with the static output config.

Changes:
- Remove EmDash from astro.config.mjs (revert to static output)
- Remove emdash packages from package.json/package-lock.json
- Remove seed/seed.json (was EmDash-only)
- Remove src/live.config.ts (EmDash Astro loader)
- Add src/content.config.ts (Astro content collection for blog)
- Move 3 blog posts to src/content/blog/*.md
- Update src/pages/index.astro to use getCollection('blog')
- Update src/pages/บทความ/[slug].astro to use render() from astro:content
  (Astro 6 API: render(article), not article.render())
- Update src/pages/บทความ/index.astro (blog list)
- Add .hermes/ to .gitignore

Verified:
- npm run build: 35 pages, complete in 2.50s
- / , /aeroflex, /about-us, /บทความ, /บทความ/welcome-post: all 200

package.json

@@ -7,17 +7,14 @@
     "dev": "astro dev",
     "build": "astro build",
     "preview": "astro preview",
-    "astro": "astro",
-    "start": "node ./dist/server/entry.mjs"
+    "astro": "astro"
   },
   "dependencies": {
     "@astrojs/check": "^0.9.4",
-    "@astrojs/node": "^10.1.1",
     "@astrojs/react": "^5.0.5",
     "@tailwindcss/typography": "^0.5.15",
     "@tailwindcss/vite": "^4.0.0",
     "astro": "^6.1.7",
-    "emdash": "^0.14.0",
     "marked": "^18.0.3",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",