feat: add custom IP/CIDR input option to policy source and destination fields with dynamic text input and placeholder examples

Add customTargetValue constant for custom IP/CIDR selection, implement endpointSelectValue helper to detect custom values not in target list, add isCustomEndpoint predicate to show/hide custom input fields, extend PolicyDesigner with "Custom IP/CIDR" dropdown option that reveals text input for manual IP/CIDR entry with trim on change, add placeholder examples "172.16.0.50 or 172.16.0.0/16" to guide user

frontend/src/pages/Policies.tsx

@@ -216,8 +216,8 @@ export function Policies() {
             <Field label="Project"><select className={selectClass} value={form.project_id} onChange={(event) => setForm({ ...form, project_id: event.target.value })}><option value="">Global</option>{(projects.data ?? []).map((project) => <option key={project.id} value={project.id}>{project.name}</option>)}</select></Field>
             <Field label="Name"><input className={inputClass} value={form.name} onChange={(event) => setForm({ ...form, name: event.target.value })} /></Field>
             <div className="grid grid-cols-2 gap-3">
-              <Field label="Source"><input className={inputClass} value={form.source} onChange={(event) => setForm({ ...form, source: event.target.value })} /></Field>
+              <Field label="Source"><input className={inputClass} value={form.source} onChange={(event) => setForm({ ...form, source: event.target.value })} placeholder="any, workload:<id>, 172.16.0.50 or 172.16.0.0/16" /></Field>
-              <Field label="Destination"><input className={inputClass} value={form.destination} onChange={(event) => setForm({ ...form, destination: event.target.value })} /></Field>
+              <Field label="Destination"><input className={inputClass} value={form.destination} onChange={(event) => setForm({ ...form, destination: event.target.value })} placeholder="any, workload:<id>, 172.16.0.53 or 172.16.10.0/24" /></Field>
             </div>
             <Field label="Service"><select className={selectClass} value={form.service_id} onChange={(event) => chooseService(event.target.value)}><option value="">Custom</option>{(services.data ?? []).map((service) => <option key={service.id} value={service.id}>{service.name} {service.ports}</option>)}</select></Field>
             <div className="grid grid-cols-2 gap-3">

frontend/src/pages/PolicyDesigner.tsx

@@ -11,6 +11,16 @@ type TargetOption = {
   value: string;
 };
 
+const customTargetValue = "__custom_ip_cidr__";
+
+function endpointSelectValue(value: string, targets: TargetOption[]) {
+  return targets.some((target) => target.value === value) ? value : customTargetValue;
+}
+
+function isCustomEndpoint(value: string, targets: TargetOption[]) {
+  return endpointSelectValue(value, targets) === customTargetValue;
+}
+
 export function PolicyDesigner() {
   const queryClient = useQueryClient();
   const workloads = useQuery({ queryKey: ["workloads"], queryFn: () => api<Workload[]>("/vms") });
@@ -35,6 +45,7 @@ export function PolicyDesigner() {
   const targets = useMemo<TargetOption[]>(() => {
     return [
       { label: "Any", value: "any" },
+      { label: "Custom IP/CIDR", value: customTargetValue },
       ...(workloads.data ?? []).map((workload) => ({ label: `VM/LXC: ${workload.name}`, value: `workload:${workload.id}` })),
       ...(securityGroups.data ?? []).map((group) => ({ label: `Security Group: ${group.name}`, value: `sg:${group.name}` })),
       ...(networks.data ?? []).map((network) => ({ label: `Network: ${network.name}`, value: `network:${network.name}` })),
@@ -115,14 +126,40 @@ export function PolicyDesigner() {
             </Field>
             <div />
             <Field label="Source">
-              <select className={selectClass} value={form.source} onChange={(event) => setForm({ ...form, source: event.target.value })}>
+              <select
+                className={selectClass}
+                value={endpointSelectValue(form.source, targets)}
+                onChange={(event) => setForm({ ...form, source: event.target.value === customTargetValue ? "" : event.target.value })}
+              >
                 {targets.map((target) => <option key={target.value} value={target.value}>{target.label}</option>)}
               </select>
+              {isCustomEndpoint(form.source, targets) ? (
+                <input
+                  className={`${inputClass} mt-2`}
+                  value={form.source}
+                  onChange={(event) => setForm({ ...form, source: event.target.value.trim() })}
+                  placeholder="172.16.0.50 or 172.16.0.0/16"
+                  required
+                />
+              ) : null}
             </Field>
             <Field label="Destination">
-              <select className={selectClass} value={form.destination} onChange={(event) => setForm({ ...form, destination: event.target.value })}>
+              <select
+                className={selectClass}
+                value={endpointSelectValue(form.destination, targets)}
+                onChange={(event) => setForm({ ...form, destination: event.target.value === customTargetValue ? "" : event.target.value })}
+              >
                 {targets.map((target) => <option key={target.value} value={target.value}>{target.label}</option>)}
               </select>
+              {isCustomEndpoint(form.destination, targets) ? (
+                <input
+                  className={`${inputClass} mt-2`}
+                  value={form.destination}
+                  onChange={(event) => setForm({ ...form, destination: event.target.value.trim() })}
+                  placeholder="172.16.0.53 or 172.16.10.0/24"
+                  required
+                />
+              ) : null}
             </Field>
             <Field label="Service">
               <select className={selectClass} value={form.service_id} onChange={(event) => chooseService(event.target.value)}>