feat: add URL deep-linking for DataGrids

- Add PageUrlState utility for URL ↔ state serialization
- Add column `id` field for unique column identification in URLs
- Update idSelector to return String for URL compatibility
- All DataGrid pages now support URL params: search, sort, order, id
- Browser URL updates via replaceState (no GoRouter rebuilds)
- Add FilterPanelSemantics for filter panel semantic IDs
- Add TESTING.md documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/features/control_room/presentation/pages/control_room_page.dart

@@ -17,11 +17,15 @@ class ControlRoomPage extends ConsumerWidget {
   const ControlRoomPage({
     super.key,
     this.nav = ControlRoomNav.containers,
+    this.routerState,
   });
 
   /// The current nav item to display.
   final ControlRoomNav nav;
 
+  /// Router state for URL deep-linking (query params).
+  final GoRouterState? routerState;
+
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     final colorScheme = Theme.of(context).colorScheme;
@@ -53,7 +57,7 @@ class ControlRoomPage extends ConsumerWidget {
           ),
           // Section content
           Expanded(
-            child: _SectionContent(nav: nav),
+            child: _SectionContent(nav: nav, routerState: routerState),
           ),
         ],
       ),
@@ -63,15 +67,16 @@ class ControlRoomPage extends ConsumerWidget {
 
 /// Renders content for the selected nav item.
 class _SectionContent extends ConsumerWidget {
-  const _SectionContent({required this.nav});
+  const _SectionContent({required this.nav, this.routerState});
 
   final ControlRoomNav nav;
+  final GoRouterState? routerState;
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
     return switch (nav) {
-      ControlRoomNav.containers => const _ContainersSection(),
-      ControlRoomNav.proxyHosts => const ProxyHostsPage(),
+      ControlRoomNav.containers => _ContainersSection(routerState: routerState),
+      ControlRoomNav.proxyHosts => ProxyHostsPage(routerState: routerState),
       _ => _PlaceholderSection(nav: nav),
     };
   }
@@ -119,7 +124,9 @@ class _PlaceholderSection extends StatelessWidget {
 
 /// Containers section with optional stack filter.
 class _ContainersSection extends ConsumerWidget {
-  const _ContainersSection();
+  const _ContainersSection({this.routerState});
+
+  final GoRouterState? routerState;
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
@@ -129,7 +136,7 @@ class _ContainersSection extends ConsumerWidget {
     return Row(
       children: [
         // Stacks filter panel
-        const _StacksFilterPanel(),
+        _StacksFilterPanel(routerState: routerState),
         // Divider
         VerticalDivider(
           width: 1,
@@ -139,7 +146,7 @@ class _ContainersSection extends ConsumerWidget {
         // Main content - containers list or stack detail
         Expanded(
           child: selectedStack == null
-              ? const ContainersListPage()
+              ? ContainersListPage(routerState: routerState)
               : StackDetailPage(stackId: selectedStack),
         ),
       ],
@@ -149,7 +156,9 @@ class _ContainersSection extends ConsumerWidget {
 
 /// Stacks filter panel for Containers section (includes "All Containers" option).
 class _StacksFilterPanel extends ConsumerWidget {
-  const _StacksFilterPanel();
+  const _StacksFilterPanel({this.routerState});
+
+  final GoRouterState? routerState;
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
@@ -207,6 +216,7 @@ class _StacksFilterPanel extends ConsumerWidget {
               data: (stacks) => _StacksList(
                 stacks: stacks,
                 selectedStackId: selectedStack,
+                routerState: routerState,
                 onStackSelected: (id) =>
                     ref.read(selectedStackProvider.notifier).select(id),
                 onStackAction: (id, action) =>
@@ -281,12 +291,14 @@ class _StacksList extends StatefulWidget {
     required this.selectedStackId,
     required this.onStackSelected,
     required this.onStackAction,
+    this.routerState,
   });
 
   final List<Stack> stacks;
   final String? selectedStackId;
   final void Function(String) onStackSelected;
   final void Function(String, String) onStackAction;
+  final GoRouterState? routerState;
 
   @override
   State<_StacksList> createState() => _StacksListState();