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>

lib/config.mjs

@@ -0,0 +1,16 @@
+import * as fs from 'node:fs';
+import yaml from 'yaml-js';
+
+let _config = null;
+
+export function get_config() {
+	if (_config !== null) { return _config; }
+	try {
+		const content = fs.readFileSync('./config.yaml', 'utf-8');
+		_config = yaml.load(content);
+	} catch (e) {
+		if (e.code === 'ENOENT') { _config = {}; }
+		else { throw e; }
+	}
+	return _config;
+}