Add bible download route and UI button for run details

- New GET /run/<id>/download_bible route serves project bible.json as attachment
- Download Bible button added to run_details.html header toolbar

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

templates/run_details.html

@@ -10,6 +10,9 @@
         <button class="btn btn-outline-primary me-2" type="button" data-bs-toggle="collapse" data-bs-target="#bibleCollapse" aria-expanded="false" aria-controls="bibleCollapse">
             <i class="fas fa-scroll me-2"></i>Show Bible
         </button>
+        <a href="{{ url_for('run.download_bible', id=run.id) }}" class="btn btn-outline-info me-2" title="Download the project bible (JSON) used for this run.">
+            <i class="fas fa-file-download me-2"></i>Download Bible
+        </a>
         <button class="btn btn-primary me-2" data-bs-toggle="modal" data-bs-target="#modifyRunModal" data-bs-toggle="tooltip" title="Create a new run based on this one, but with different instructions (e.g. 'Make it darker').">
             <i class="fas fa-pen-fancy me-2"></i>Modify & Re-run
         </button>