Add Gitea markdown rendering and Edit/Preview tabs

- New /api/render-markdown proxy to Gitea (configured via config.yaml)
- lib/config.mjs loads config.yaml with yaml-js
- Edit/Preview tabs on the body field in the task dialog
- Title and body rendered as markdown inline in the task list
- Gitea markup+chroma CSS extracted and vendored to public/gitea-markup.css
- Markdown cached in memory per text string

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -9,6 +9,7 @@
 		"start": "node server.mjs"
 	},
 	"dependencies": {
-		"express": "^5.2.1"
+		"express": "^5.2.1",
+		"yaml-js": "^0.3.1"
 	}
 }