fix: remove qemu-utils from installer + configurable storage path

1. Removed qemu-utils from required packages — Proxmox ships its own
   qemu-img and installing Debian's version breaks VMs. Added preflight
   check: if qemu-img missing, exits with clear error message.

2. Installer now prompts for host storage path (default:
   /mnt/pve/hosted-thin). Uses it for the LXC bind mount mp0.
   The LXC always sees /mnt/converter internally — no symlinks needed.

backend/install.sh

@@ -48,6 +48,10 @@ if ! command -v git &>/dev/null; then
     echo "  Installing git..."
     apt-get update -qq && apt-get install -y -qq git
 fi
+if ! command -v qemu-img &>/dev/null; then
+    echo "  ${RED}✗${NC} 'qemu-img' not found — Proxmox ships this. Do NOT install qemu-utils (conflicts with Proxmox)."
+    exit 1
+fi
 echo "  ${GREEN}✓${NC} Running on Proxmox host."
 
 # ───────────────────────────────────────────────────────────────────
@@ -105,11 +109,10 @@ PACKAGES=()
 REQUIRED=(
     python3            "python3"
     python3-pip        "pip3"
-    qemu-utils         "qemu-img"
     libguestfs-tools   "guestfish"
     p7zip-full         "7z"
     unzip              "unzip"
-    unrar-free          "unrar"
+    unrar-free         "unrar"
     tar                "tar"
     gzip               "gunzip"
     bzip2              "bunzip2"
@@ -216,6 +219,23 @@ CT_MAC="${CT_MAC:-BC:24:11:80:5A:B1}"
 NET_CFG="name=eth0,bridge=${CT_BRIDGE},firewall=1,gw=${CT_GW},hwaddr=${CT_MAC},ip=${CT_IP},type=veth"
 ROOTFS="local-lvm:vm-${CTID}-disk-0,size=24G"
 
+# ── Storage path ──────────────────────────────────────────────────
+echo ""
+echo "  ${CYAN}Storage mount:${NC}"
+echo "    Path on the Proxmox host where VM Bench stores its data."
+echo "    The LXC will see this as /mnt/converter internally."
+read -p "    Host storage path [/mnt/pve/hosted-thin]: " STORAGE_PATH
+STORAGE_PATH="${STORAGE_PATH:-/mnt/pve/hosted-thin}"
+
+# Remove trailing slash
+STORAGE_PATH="${STORAGE_PATH%/}"
+
+# Create the directory on the host if it doesn't exist
+if [ ! -d "$STORAGE_PATH" ]; then
+    echo "  Creating: $STORAGE_PATH"
+    mkdir -p "$STORAGE_PATH"
+fi
+
 # ── Template selection ────────────────────────────────────────────
 echo ""
 echo "  ${CYAN}Available Debian templates:${NC}"
@@ -260,7 +280,7 @@ pct create "$CTID" "$TEMPLATE" \
     --swap 2048 \
     --unprivileged 0 \
     --features nesting=1 \
-    --mp0 /mnt/converter,mp=/mnt/converter \
+    --mp0 ${STORAGE_PATH},mp=/mnt/converter \
     --onboot 1 \
     --start 0