Configure site for /cg-ai subdirectory deployment

- Set base path to '/cg-ai' in astro.config.mjs
- Update favicon to use metagov.png with dynamic base path
- Add deployment documentation for subdirectory configuration
- Rebuild dist with correct asset paths

CSS and other assets will now load correctly when deployed
to example.com/cg-ai/

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

astro.config.mjs

@@ -2,4 +2,6 @@
 import { defineConfig } from 'astro/config';
 
 // https://astro.build/config
-export default defineConfig({});
+export default defineConfig({
+	base: '/cg-ai',
+});