viewer on-demand — relancer viser à la demande depuis le dashboard

Le viser de demo.py était tué dès que le PLY était écrit (pour libérer la VRAM),
donc les liens dans le dashboard menaient vers ERR_CONNECTION_REFUSED.

Ajout d'un viewer standalone indépendant :
- scripts/viser_ply.py : charge un PLY via open3d + sert via viser (sans GPU),
  subsample random à 2M pts max pour rester fluide
- app/main.py : routes POST /jobs/{id}/view et /stitches/{id}/view qui scp
  le script sur le worker et lancent un viser détaché (nohup+setsid+disown via
  wrapper shell déposé sur le worker)
- templates : remplace <a href> par <button class=viewer-btn> qui POST puis
  window.open de l'URL retournée
- Dockerfile : copie scripts/ dans l'image (nécessaire pour scp-er viser_ply.py)

app/main.py

@@ -310,3 +310,81 @@ async def retry_stitch(stitch_id: int):
             (stitch_id,),
         )
     return {"ok": True}
+
+
+VIEWER_PORT_BASE = 8200
+VIEWER_SCRIPT_REMOTE = "/tmp/cosma-viser_ply.py"
+
+
+def _worker_by_host(host: str) -> dict | None:
+    for w in WORKERS:
+        if w["host"] == host:
+            return w
+    return WORKERS[0] if WORKERS else None
+
+
+async def _launch_viewer(worker: dict, ply_path: str, port: int) -> None:
+    alias = worker["ssh_alias"]
+    local_script = Path(__file__).parent.parent / "scripts" / "viser_ply.py"
+    proc = await asyncio.create_subprocess_exec(
+        "scp", "-o", "BatchMode=yes", str(local_script), f"{alias}:{VIEWER_SCRIPT_REMOTE}",
+        stdout=asyncio.subprocess.DEVNULL, stderr=asyncio.subprocess.PIPE,
+    )
+    _, err = await proc.communicate()
+    if proc.returncode != 0:
+        raise HTTPException(500, f"scp viser_ply.py failed: {err.decode()[:200]}")
+    wrapper = (
+        f"#!/bin/bash\n"
+        f"pkill -f 'viser_ply.py.*--port {port}' 2>/dev/null\n"
+        f"sleep 1\n"
+        f"cd /home/floppyrj45/ai-video/lingbot-map\n"
+        f"source .venv/bin/activate\n"
+        f"exec python3 {VIEWER_SCRIPT_REMOTE} {ply_path!r} --port {port} --downsample 0\n"
+    )
+    wrapper_path = f"/tmp/cosma-viser-launch-{port}.sh"
+    proc = await asyncio.create_subprocess_exec(
+        "ssh", "-o", "BatchMode=yes", alias,
+        f"cat > {wrapper_path} && chmod +x {wrapper_path}",
+        stdin=asyncio.subprocess.PIPE,
+        stdout=asyncio.subprocess.DEVNULL, stderr=asyncio.subprocess.PIPE,
+    )
+    _, err = await proc.communicate(wrapper.encode())
+    if proc.returncode != 0:
+        raise HTTPException(500, f"wrapper write failed: {err.decode()[:200]}")
+    proc = await asyncio.create_subprocess_exec(
+        "ssh", "-o", "BatchMode=yes", alias,
+        f"setsid nohup {wrapper_path} </dev/null >/tmp/cosma-viser-{port}.log 2>&1 & disown; sleep 0.3",
+        stdout=asyncio.subprocess.DEVNULL, stderr=asyncio.subprocess.PIPE,
+    )
+    await proc.communicate()
+    await asyncio.sleep(5)
+
+
+@app.post("/jobs/{job_id}/view")
+async def view_job(job_id: int):
+    with closing(db()) as conn:
+        row = conn.execute(
+            "SELECT ply_path, worker_host FROM jobs WHERE id=? AND status='done'",
+            (job_id,),
+        ).fetchone()
+    if not row or not row["ply_path"]:
+        raise HTTPException(404, "PLY non disponible")
+    worker = _worker_by_host(row["worker_host"]) or WORKERS[0]
+    port = VIEWER_PORT_BASE + job_id
+    await _launch_viewer(worker, row["ply_path"], port)
+    return {"url": f"http://{worker['host']}:{port}"}
+
+
+@app.post("/stitches/{stitch_id}/view")
+async def view_stitch(stitch_id: int):
+    with closing(db()) as conn:
+        row = conn.execute(
+            "SELECT output_ply, worker_host FROM stitches WHERE id=? AND status='done'",
+            (stitch_id,),
+        ).fetchone()
+    if not row or not row["output_ply"]:
+        raise HTTPException(404, "PLY stitch non disponible")
+    worker = _worker_by_host(row["worker_host"]) or WORKERS[0]
+    port = VIEWER_PORT_BASE + 1000 + stitch_id
+    await _launch_viewer(worker, row["output_ply"], port)
+    return {"url": f"http://{worker['host']}:{port}"}