fix: feat: quickstart guide and architecture docs on disinto.ai (#394)

Add two documentation pages to the site:
- site/docs/quickstart.html — prerequisites, disinto init walkthrough,
  first issue lifecycle demo
- site/docs/architecture.html — agent loop diagram, phase protocol,
  vault/quality gate, planner+predictor feedback cycle

Both pages are linked from the landing page navigation and footer.
Sitemap updated with new URLs.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

site/index.html

@@ -527,6 +527,8 @@
     <div class="cta">
       <p>The code is public. The factory is running. See for yourself.</p>
       <div class="cta-links">
+        <a href="/docs/quickstart">Quickstart</a>
+        <a href="/docs/architecture">Architecture</a>
         <a href="https://codeberg.org/johba/disinto">Browse the source</a>
         <a href="https://codeberg.org/johba/disinto/issues">Watch it work</a>
         <a href="/dashboard">Live dashboard</a>
@@ -536,7 +538,9 @@
     <div class="footer">
       <div>Built from scrap, powered by a single battery.</div>
       <div class="links">
-        <a href="https://codeberg.org/johba/disinto">codeberg.org/johba/disinto</a>
+        <a href="/docs/quickstart">quickstart</a>
+        <a href="/docs/architecture">architecture</a>
+        <a href="https://codeberg.org/johba/disinto">source</a>
         <a href="/dashboard">dashboard</a>
       </div>
       <div class="under-hood">