fix(FN-2198): sync agent heartbeat config UI with live runtime updates

- Refresh AgentDetailView on agent:updated SSE events while preserving local unsaved config edits
- Resync heartbeat and budget form state from latest runtime config when agent data changes
- Centralize heartbeat interval defaults/formatting in shared utilities and reuse them in AgentsView selectors
- Add dashboard tests for default heartbeat hints, unset runtime fallback behavior, and custom interval options

packages/dashboard/app/utils/heartbeatIntervals.ts

@@ -0,0 +1,46 @@
+export const DEFAULT_HEARTBEAT_INTERVAL_MS = 3_600_000;
+
+export const HEARTBEAT_INTERVAL_PRESETS = [
+  { value: 1000, label: "1s" },
+  { value: 5000, label: "5s" },
+  { value: 10000, label: "10s" },
+  { value: 30000, label: "30s" },
+  { value: 60000, label: "1m" },
+  { value: 300000, label: "5m" },
+  { value: 900000, label: "15m" },
+  { value: 1800000, label: "30m" },
+  { value: 3600000, label: "1h" },
+  { value: 10800000, label: "3h" },
+  { value: 21600000, label: "6h" },
+  { value: 43200000, label: "12h" },
+  { value: 86400000, label: "24h" },
+] as const;
+
+export function formatHeartbeatInterval(ms: number): string {
+  if (ms < 1000) return `${ms}ms`;
+  if (ms < 60_000) return `${Math.round(ms / 1000)}s`;
+  if (ms < 3_600_000) return `${Math.round(ms / 60_000)}m`;
+  return `${Math.round(ms / 3_600_000)}h`;
+}
+
+export function resolveHeartbeatIntervalMs(intervalMs: unknown): number {
+  if (typeof intervalMs !== "number" || !Number.isFinite(intervalMs)) {
+    return DEFAULT_HEARTBEAT_INTERVAL_MS;
+  }
+
+  return Math.max(1000, Math.round(intervalMs));
+}
+
+export function getHeartbeatIntervalOptions(currentIntervalMs: number): Array<{ value: number; label: string }> {
+  if (HEARTBEAT_INTERVAL_PRESETS.some((preset) => preset.value === currentIntervalMs)) {
+    return [...HEARTBEAT_INTERVAL_PRESETS];
+  }
+
+  const customOption = {
+    value: currentIntervalMs,
+    label: `${formatHeartbeatInterval(currentIntervalMs)} (custom)`,
+  };
+
+  return [...HEARTBEAT_INTERVAL_PRESETS, customOption]
+    .sort((a, b) => a.value - b.value);
+}