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.

frontend/src/routes/+layout.svelte

@@ -104,6 +104,7 @@
 			targets_slack: targets.filter(t => t.type === 'slack').length,
 			targets_ntfy: targets.filter(t => t.type === 'ntfy').length,
 			targets_matrix: targets.filter(t => t.type === 'matrix').length,
+			targets_broadcast: targets.filter(t => t.type === 'broadcast').length,
 		} as Record<string, number>;
 	});
 
@@ -169,6 +170,7 @@
 				{ href: '/targets?type=slack', key: 'nav.targetSlack', icon: 'mdiSlack', countKey: 'targets_slack' },
 				{ href: '/targets?type=ntfy', key: 'nav.targetNtfy', icon: 'mdiBell', countKey: 'targets_ntfy' },
 				{ href: '/targets?type=matrix', key: 'nav.targetMatrix', icon: 'mdiMatrix', countKey: 'targets_matrix' },
+				{ href: '/targets?type=broadcast', key: 'nav.targetBroadcast', icon: 'mdiBullhorn', countKey: 'targets_broadcast' },
 			],
 		},
 	];