feat: add input validation to search, update agent card layout, and extend ProfileFormField with input constraints

lib/features/agents/presentation/screens/agent_search_screen.dart

@@ -187,6 +187,7 @@ class _AgentSearchScreenState extends ConsumerState<AgentSearchScreen> {
                       ),
                     ),
                     onSubmitted: (value) {
+                      if (value.trim().isEmpty) return;
                       ref.read(searchAgentsProvider.notifier).search(value);
                     },
                   ),
@@ -196,13 +197,24 @@ class _AgentSearchScreenState extends ConsumerState<AgentSearchScreen> {
             const SizedBox(width: 0),
             GestureDetector(
               onTap: () {
-                ref
-                    .read(searchAgentsProvider.notifier)
-                    .search(_searchController.text);
+                final query = _searchController.text.trim();
+                if (query.isEmpty) {
+                  // No input — don't trigger a refresh
+                  ScaffoldMessenger.of(context).showSnackBar(
+                    const SnackBar(
+                      content: Text('Please enter a keyword'),
+                      behavior: SnackBarBehavior.floating,
+                      duration: Duration(seconds: 2),
+                    ),
+                  );
+                  return;
+                }
+                ref.read(searchAgentsProvider.notifier).search(query);
               },
               child: Container(
                 width: 62,
                 height: 42,
+                alignment: Alignment.center,
                 decoration: BoxDecoration(
                   color: AppColors.accentOrange,
                   border: Border.all(
@@ -211,12 +223,10 @@ class _AgentSearchScreenState extends ConsumerState<AgentSearchScreen> {
                   ),
                   borderRadius: BorderRadius.circular(7),
                 ),
-                child: Center(
-                  child: SvgPicture.string(
-                    '<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg"><path d="M15.5 14h-.79l-.28-.27A6.471 6.471 0 0 0 16 9.5 6.5 6.5 0 1 0 9.5 16c1.61 0 3.09-.59 4.23-1.57l.27.28v.79l5 4.99L20.49 19l-4.99-5zm-6 0C7.01 14 5 11.99 5 9.5S7.01 5 9.5 5 14 7.01 14 9.5 11.99 14 9.5 14z" fill="white"/></svg>',
-                    width: 24,
-                    height: 24,
-                  ),
+                child: const Icon(
+                  Icons.search,
+                  color: Colors.white,
+                  size: 24,
                 ),
               ),
             ),