fix: real-time progress during qemu-img convert, smoother percentages

qemu-img convert is the longest step but previously had no progress
updates — bar stuck at 10% until conversion completed.

Now _convert_with_progress() runs qemu-img in background and polls
output file size every 2s, updating progress with GiB done/total.

Progress flow for single disk:
  5% queued → 10% starting → 10-55% converting (real-time)
  → 60% shrinking → 70% creating VM → 75-85% importing
  → 95% configuring → 100% done

backend/provisioner.py

@@ -145,6 +145,43 @@ def _run(cmd: list[str], check: bool = True, timeout: int = 3600) -> subprocess.
     return result
 
 
+def _convert_with_progress(
+    job_id: str, source_path: Path, output_path: Path, format: str,
+    start_pct: int, end_pct: int,
+):
+    """Run qemu-img convert in background and update job progress
+    by polling the output file size against the source virtual size."""
+    # Get source virtual size for percentage estimation
+    info = _run(["qemu-img", "info", "--output=json", str(source_path)])
+    source_size = json.loads(info.stdout).get("virtual-size", 0)
+    if source_size == 0:
+        source_size = source_path.stat().st_size
+
+    proc = subprocess.Popen(
+        ["qemu-img", "convert", "-f", format, "-O", "qcow2",
+         str(source_path), str(output_path)],
+        stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
+    )
+
+    # Poll output file size and update progress
+    while proc.poll() is None:
+        time.sleep(2)
+        if output_path.exists():
+            current = output_path.stat().st_size
+            if source_size > 0:
+                ratio = min(current / source_size, 1.0)
+                pct = start_pct + int(ratio * (end_pct - start_pct))
+                gb_done = current / (1024**3)
+                gb_total = source_size / (1024**3)
+                _update_job(job_id, progress=pct,
+                            message=f"Converting disk... {gb_done:.1f} / {gb_total:.1f} GiB")
+
+    if proc.returncode != 0:
+        raise RuntimeError(f"qemu-img convert failed (rc={proc.returncode})")
+
+    _update_job(job_id, progress=end_pct, message="Disk converted.")
+
+
 def _process_job(job_id: str, req: JobSubmissionRequest):
     try:
         vmid = req.vmid
@@ -171,13 +208,11 @@ def _process_job(job_id: str, req: JobSubmissionRequest):
                 logger.info("Disk %d: source=%s format=%s size=%.1f GiB",
                             idx, source_path, disk.format, disk.size_gb)
 
-                _run(["qemu-img", "convert",
+                # Convert with real-time progress
-                      "-f", disk.format,
+                _convert_with_progress(
-                      "-O", "qcow2",
+                    job_id, source_path, output_path, disk.format,
-                      str(source_path), str(output_path)],
+                    start_pct=10 + idx * 10, end_pct=55 + idx * 10,
-                     timeout=7200)
+                )
-                _update_job(job_id, progress=20 + (idx + 1) * 15,
-                            message=f"Converted disk {idx + 1}/{len(disk_specs)}")
             else:
                 size_gb = spec.size_gb or 32
                 logger.info("Creating empty disk %d: %d GiB", idx, size_gb)
@@ -204,7 +239,7 @@ def _process_job(job_id: str, req: JobSubmissionRequest):
                 target_gb = int(round(current_gb)) + 1
 
             if target_gb < current_gb:
-                _update_job(job_id, progress=65,
+                _update_job(job_id, progress=60,
                             message=f"Shrinking disk to {target_gb} GiB...")
                 logger.info("Shrinking disk: %.1f GiB → %d GiB via virt-resize", current_gb, target_gb)
                 try:
@@ -276,6 +311,7 @@ def _process_job(job_id: str, req: JobSubmissionRequest):
                   f"{req.target_storage}:0,format=raw,size=4M"])
 
         # ── Finalise ───────────────────────────────────────────────
+        _update_job(job_id, progress=95, message="Configuring VM...")
         _run(["qm", "set", str(vmid), "--boot", "order=scsi0"])
         _run(["qm", "set", str(vmid), "--serial0", "socket"])