Analyse STL/3MF on upload: bounding box + volume, cached in stl_cache

- StlCache model: filename, cube_x/y/z (mm), volume_ccm
- Migration 0007: stl_cache table
- app/stl_analysis.py: trimesh-based analyse() + get_cache_map()
  - Runs immediately after upload in both /jobs and /brackets/{id}/jobs
  - Skips .gcode (no geometry), caches per filename, idempotent
- Library selector in both modals now shows dimensions and volume
- requirements: trimesh==4.5.3

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

app/templates/jobs.html

@@ -129,7 +129,8 @@
                 <select name="stl_select" class="form-select bg-dark border-secondary text-white">
                   <option value="">— select file —</option>
                   {% for f in stl_files %}
-                  <option value="{{ f }}">{{ f }}</option>
+                  {% set c = stl_cache.get(f) %}
+                  <option value="{{ f }}">{{ f }}{% if c %} — {{ c.cube_x|round(1) }}×{{ c.cube_y|round(1) }}×{{ c.cube_z|round(1) }} mm · {{ c.volume_ccm }} cm³{% endif %}</option>
                   {% endfor %}
                 </select>
                 {% else %}