feat(cron): dynamic delivery options from API instead of hardcoded select

Replace the hardcoded 4-option deliver dropdown (local/discord/telegram/slack)
with a dynamic select populated from a new GET /api/crons/delivery-options
endpoint that reads _KNOWN_DELIVERY_PLATFORMS from hermes-agent.

Key changes:
- Add GET /api/crons/delivery-options endpoint returning all known platforms
- Frontend loads options asynchronously on first cron form open, with caching
- Enable deliver editing for existing jobs (was previously disabled)
- Include deliver in update payload when editing cron jobs
- Fallback to local-only if API unavailable
- Custom deliver values (e.g. feishu:oc_xxx) shown with * suffix
- Add cron_deliver_custom i18n key to all 12 locales
- Add 5 integration tests for the new endpoint

api/routes.py

@@ -4781,6 +4781,12 @@ def handle_get(handler, parsed) -> bool:
         with cron_profile_context():
             return _handle_cron_status(handler, parsed)
 
+    if parsed.path == "/api/crons/delivery-options":
+        from api.profiles import cron_profile_context
+
+        with cron_profile_context():
+            return _handle_cron_delivery_options(handler)
+
     # ── Skills API (GET) ──
     if parsed.path == "/api/skills":
         qs = parse_qs(parsed.query)
@@ -9515,6 +9521,21 @@ def _handle_cron_create(handler, body):
         return j(handler, {"error": str(e)}, status=400)
 
 
+def _handle_cron_delivery_options(handler):
+    """Return available delivery platforms for cron jobs."""
+    try:
+        from cron.scheduler import _KNOWN_DELIVERY_PLATFORMS
+    except Exception:
+        _KNOWN_DELIVERY_PLATFORMS = frozenset()
+    platforms = [
+        {"value": "local", "label": "Local (save output only)"},
+        {"value": "origin", "label": "Origin (reply to creator)"}
+    ]
+    for name in sorted(_KNOWN_DELIVERY_PLATFORMS):
+        platforms.append({"value": name, "label": name.capitalize()})
+    return j(handler, {"platforms": platforms})
+
+
 def _handle_cron_update(handler, body):
     try:
         require(body, "job_id")