Add webhook trigger condition for automations

Per-automation webhook URL with auto-generated 128-bit hex token.
External services (Home Assistant, IFTTT, curl) can POST to
/api/v1/webhooks/{token} with {"action": "activate"|"deactivate"}
to control automation state — no API key required (token is auth).

Backend: WebhookCondition model, engine state tracking with
immediate evaluation, webhook endpoint, schema/route updates.
Frontend: webhook option in condition editor, URL display with
copy button, card badge, i18n for en/ru/zh.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/css/automations.css

@@ -270,3 +270,34 @@
     color: var(--text-muted);
     text-align: center;
 }
+
+/* Webhook URL row */
+.webhook-url-row {
+    display: flex;
+    gap: 6px;
+    align-items: center;
+}
+
+.webhook-url-row input {
+    flex: 1;
+    padding: 6px 8px;
+    border: 1px solid var(--border-color);
+    border-radius: 4px;
+    background: var(--bg-color);
+    color: var(--text-color);
+    font-size: 0.8rem;
+    font-family: monospace;
+}
+
+.btn-webhook-copy {
+    white-space: nowrap;
+    padding: 6px 12px !important;
+    font-size: 0.8rem !important;
+}
+
+.webhook-save-hint {
+    color: var(--text-muted);
+    font-size: 0.85rem;
+    font-style: italic;
+    margin: 4px 0 0;
+}