Create client ids without crypto.randomUUID

crypto.randomUUID() is only defined in secure contexts (HTTPS or
localhost). Opened over plain HTTP from another machine in the LAN, the
circuit list editor failed with "crypto.randomUUID is not a function"
whenever it created a circuit, device row, circuit group or distribution
board component, including typing into the -frei- row.

createClientId() uses crypto.randomUUID() where available and otherwise
builds an RFC 4122 version 4 UUID from crypto.getRandomValues(), which
works in every context. AGENTS.md notes the rule.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/frontend/utils/client-id.ts

@@ -0,0 +1,27 @@
+/**
+ * Creates a random RFC 4122 version 4 UUID for new entities built in the
+ * browser.
+ *
+ * crypto.randomUUID() exists only in secure contexts (HTTPS or localhost).
+ * The app is also opened over plain HTTP from other machines in the LAN, where
+ * it is undefined, so fall back to crypto.getRandomValues(), which is
+ * available in every context.
+ */
+export function createClientId(
+  source: Pick<Crypto, "getRandomValues"> & Partial<Pick<Crypto, "randomUUID">> = crypto
+): string {
+  if (typeof source.randomUUID === "function") {
+    return source.randomUUID();
+  }
+  const bytes = source.getRandomValues(new Uint8Array(16));
+  bytes[6] = (bytes[6] & 0x0f) | 0x40; // version 4
+  bytes[8] = (bytes[8] & 0x3f) | 0x80; // RFC 4122 variant
+  const hex = Array.from(bytes, (byte) => byte.toString(16).padStart(2, "0")).join("");
+  return [
+    hex.slice(0, 8),
+    hex.slice(8, 12),
+    hex.slice(12, 16),
+    hex.slice(16, 20),
+    hex.slice(20),
+  ].join("-");
+}