fix: pct_create make vmid optional, fix dhcp+gw, longer boot settle

Follow-ups found while verifying the approve→provision path end to end:
- vmid is now optional: the early required-field check rejected vmid:0
  before the cluster VMID guard could auto-assign a free id. Only hostname
  is required now; 0 (or a collision) resolves to `pvesh get /cluster/nextid`.
- net0: use ip=dhcp with no gateway when no static IP is given (Proxmox
  rejects gw alongside dhcp); only attach gw for a static CIDR.
- bump post-create settle to 10s so a DHCP lease is up before apt runs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

internal/httpapi/phase3.go

@@ -230,10 +230,12 @@ func executeApprovedAction(ctx context.Context, pool *db.Pool, execID uuid.UUID,
 			emitExecutionEvent(ctx, pool, execID, "failed", map[string]any{"target": targetSlug, "error": err.Error()})
 			return
 		}
-		if cfg.VMID == 0 || cfg.Hostname == "" {
+		// Only hostname is required. vmid is optional — when 0 (or later found
+		// to collide) the VMID guard below assigns a free cluster id.
+		if cfg.Hostname == "" {
 			pool.Exec(ctx, `UPDATE executions SET status='failed', result=$2::jsonb WHERE entity_id=$1`,
-				execID, `{"error":"pct_create: vmid and hostname are required"}`)
+				execID, `{"error":"pct_create: hostname is required"}`)
-			emitExecutionEvent(ctx, pool, execID, "failed", map[string]any{"target": targetSlug, "error": "missing vmid or hostname"})
+			emitExecutionEvent(ctx, pool, execID, "failed", map[string]any{"target": targetSlug, "error": "missing hostname"})
 			return
 		}
 		if cfg.Cores == 0 {
@@ -329,11 +331,23 @@ func executeApprovedAction(ctx context.Context, pool *db.Pool, execID uuid.UUID,
 			nestingFlag = fmt.Sprintf(" --features %s", strings.Join(features, ","))
 		}
 
+		// net0: DHCP when no static IP is given (or ip=="dhcp"). Proxmox
+		// rejects a gateway alongside ip=dhcp, so only add gw for a static IP.
+		net0 := "name=eth0,bridge=vmbr0,"
+		if cfg.IP == "" || strings.EqualFold(cfg.IP, "dhcp") {
+			net0 += "ip=dhcp"
+		} else {
+			net0 += "ip=" + cfg.IP
+			if cfg.GW != "" {
+				net0 += ",gw=" + cfg.GW
+			}
+		}
+
 		templatePath := fmt.Sprintf("/var/lib/vz/template/cache/%s", cfg.Template)
 		createCmd := fmt.Sprintf(
-			"pct create %d %s --hostname %s --cores %d --memory %d --rootfs %s:%d %s --net0 name=eth0,bridge=vmbr0,ip=%s,gw=%s%s --start 1",
+			"pct create %d %s --hostname %s --cores %d --memory %d --rootfs %s:%d %s --net0 %s%s --start 1",
 			cfg.VMID, templatePath, cfg.Hostname, cfg.Cores, cfg.Memory,
-			cfg.Storage, cfg.DiskGB, privFlag, cfg.IP, cfg.GW, nestingFlag)
+			cfg.Storage, cfg.DiskGB, privFlag, net0, nestingFlag)
 
 		if cfg.Nameserver != "" {
 			createCmd += fmt.Sprintf(" --nameserver %s", cfg.Nameserver)
@@ -358,8 +372,9 @@ func executeApprovedAction(ctx context.Context, pool *db.Pool, execID uuid.UUID,
 		// with a boot settle; failures are appended to output and mark the
 		// execution failed so the operator sees exactly which step broke.
 		if err == nil && (len(cfg.Services) > 0 || cfg.PostInstall != "") {
-			// Give the container a moment to finish booting before exec.
+			// Give the container time to boot and (for DHCP) acquire a lease
-			steps := []string{fmt.Sprintf("sleep 5")}
+			// before apt needs the network.
+			steps := []string{"sleep 10"}
 			if len(cfg.Services) > 0 {
 				pkgs := strings.Join(sanitizePkgs(cfg.Services), " ")
 				steps = append(steps, fmt.Sprintf("pct exec %d -- bash -lc 'apt-get update -qq && DEBIAN_FRONTEND=noninteractive apt-get install -y -qq %s'", cfg.VMID, pkgs))