chore: scaffold Astro Starlight project

- Astro 6.3 + Starlight 0.39
- TypeScript strict
- Sitemap integration
- Inter + JetBrains Mono variable fonts
- Custom .gitignore (no AI artifacts; no .env)
- .editorconfig

.gitignore

@@ -0,0 +1,32 @@
+# build output
+dist/
+.astro/
+
+# deps
+node_modules/
+
+# logs / env
+*.log
+.env
+.env.*
+!.env.example
+
+# OS
+.DS_Store
+Thumbs.db
+
+# editors
+.idea/
+.vscode/
+*.swp
+
+# AI assistant artifacts — NOT committed to the public repo
+.claude/
+CLAUDE.md
+AGENTS.md
+GEMINI.md
+.cursor/
+.aider*
+
+# local-only screenshot creds
+tools/screenshots/.env