fix: don't encode slashes in doc path fetch

encodeURIComponent turns devlog/001-self-publishing-docs.md into
devlog%2F001-self-publishing-docs.md, breaking nested paths

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

Co-Authored-By: Claude Opus 4.5 <[e-mail]>

site/app.js

···
     }
 
     try {
-      const md = await fetchText(`./docs/${encodeURIComponent(activePath)}`);
+      const md = await fetchText(`./docs/${activePath}`);
       const html = globalThis.marked.parse(md);
       contentEl.innerHTML = html;