feat: broadcast notification target + UX improvements

Add broadcast target type that fans out notifications to multiple
child targets. Dispatch expands broadcast into children in
load_link_data() — dispatcher stays unaware. Children can be
toggled on/off via disabled_child_ids in config.

Also: dashboard provider card smaller font for names, scroll-to-form
on target edit, broadcast nav tab with counter, flag_modified fix
for JSON column updates, CLAUDE.md nav tree docs.

packages/server/src/notify_bridge_server/services/notifier.py

@@ -309,11 +309,35 @@ async def send_to_receiver(target: NotificationTarget, receiver_config: dict, me
 
 
 async def send_test_notification(target: NotificationTarget, locale: str = "en") -> dict:
-    """Send a simple test message."""
+    """Send a simple test message. For broadcast targets, fans out to all children."""
+    if target.type == "broadcast":
+        return await _send_broadcast_test(target, locale)
     message = _get_test_message(locale, target.type)
     return await send_to_target(target, message)
 
 
+async def _send_broadcast_test(target: NotificationTarget, locale: str) -> dict:
+    """Send test notifications to all child targets of a broadcast target."""
+    child_ids = target.config.get("child_target_ids", [])
+    if not child_ids:
+        return {"success": False, "error": "No child targets configured"}
+
+    disabled_ids = set(target.config.get("disabled_child_ids", []))
+    engine = get_engine()
+    results: list[dict] = []
+    async with AsyncSession(engine) as session:
+        for child_id in child_ids:
+            if child_id in disabled_ids:
+                continue
+            child = await session.get(NotificationTarget, child_id)
+            if not child or child.type == "broadcast":
+                continue
+            message = _get_test_message(locale, child.type)
+            results.append(await send_to_target(child, message))
+
+    return _aggregate(results)
+
+
 async def send_test_template_notification(
     target: NotificationTarget, slot: str, template_str: str
 ) -> dict: