Add .gitignore, robots.txt, and sitemap integration

Move and restructure BaseLayout to src/layouts with SEO meta tags Add
404 page with accessibility improvements Restructure pages to src/pages

.gitignore

@@ -0,0 +1,41 @@
+# Build output
+dist/
+.astro/
+
+# Dependencies
+node_modules/
+
+# Logs
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+pnpm-debug.log*
+
+# Environment variables
+.env
+.env.local
+.env.production
+.env.*.local
+
+# macOS
+.DS_Store
+
+# IDE
+.vscode/
+.idea/
+*.swp
+*.swo
+*~
+
+# OS
+Thumbs.db
+
+# Package lock files (keep package-lock.json but ignore others)
+yarn.lock
+pnpm-lock.yaml
+
+# Local development
+*.local
+
+# Build artifacts
+*.tsbuildinfo