dashboard — bouton live (viser natif demo.py) + PLY (fallback viser_ply)

live button:
- POST /jobs/{id}/live
- Probe le port natif (worker viser_port_base + job_id) via nc
- 200 + viser_url si demo.py encore alive (necessite le patch keep-alive)
- 410 + fallback message si ferme

PLY button:
- POST /jobs/{id}/view (existant)
- Lance viser_ply.py standalone sur port VIEWER_PORT_BASE+id

Permet de choisir entre viser natif (PointCloudViewer de lingbot-map avec
camera frustums, filtre confiance interactif, animation) et viewer basic
XYZ+RGB uniquement.

app/templates/_jobs_table.html

@@ -23,7 +23,8 @@
               <span class="prog-wrap"><span class="prog-fill" style="width:{{ j.progress }}%"></span><span class="prog-text">{{ j.progress }}%</span></span>
             {% endif %}
             {% if j.status == 'done' and j.ply_path %}
-              <button class="ext viewer-btn" data-view-url="jobs/{{ j.id }}/view">viser</button>
+              <button class="ext viewer-btn" data-view-url="jobs/{{ j.id }}/live" title="viser natif de demo.py (camera frustums, filtre confiance) — si encore alive">live</button>
+              <button class="ext viewer-btn" data-view-url="jobs/{{ j.id }}/view" title="viser_ply.py standalone — toujours dispo">PLY</button>
             {% endif %}
           </span>
           <span class="dur">{{ j._duration }}</span>