feat: add search functionality for formulas by name and tags

lib/ai/formula_list.dart

@@ -3,7 +3,7 @@ import 'package:d4rt_formulas/formula_models.dart';
 import '../corpus.dart';
 import 'formula_screen.dart';
 
-class FormulaList extends StatelessWidget {
+class FormulaList extends StatefulWidget {
   final Corpus corpus;
   final List<Formula> formulas;
 
@@ -13,27 +13,84 @@ class FormulaList extends StatelessWidget {
     required this.formulas,
   });
 
+  @override
+  State<FormulaList> createState() => _FormulaListState();
+}
+
+class _FormulaListState extends State<FormulaList> {
+  final TextEditingController _searchController = TextEditingController();
+  String _searchQuery = '';
+
+  @override
+  void initState() {
+    super.initState();
+    _searchController.addListener(_onSearchChanged);
+  }
+
+  void _onSearchChanged() {
+    setState(() {
+      _searchQuery = _searchController.text.toLowerCase();
+    });
+  }
+
+  @override
+  void dispose() {
+    _searchController.dispose();
+    super.dispose();
+  }
+
+  List<Formula> get _filteredFormulas {
+    if (_searchQuery.isEmpty) return widget.formulas;
+    
+    return widget.formulas.where((formula) {
+      final nameMatch = formula.name.toLowerCase().contains(_searchQuery);
+      final tagMatch = formula.tags.any((tag) => tag.toLowerCase().contains(_searchQuery));
+      return nameMatch || tagMatch;
+    }).toList();
+  }
+
   @override
   Widget build(BuildContext context) {
-    return ListView.builder(
+    return Column(
-      itemCount: formulas.length,
+      children: [
-      itemBuilder: (context, index) {
+        Padding(
-        final formula = formulas[index];
+          padding: const EdgeInsets.all(16.0),
-        return ListTile(
+          child: TextField(
-          title: Text(formula.name),
+            controller: _searchController,
-          onTap: () {
+            decoration: const InputDecoration(
-            Navigator.push(
+              labelText: 'Search formulas',
-              context,
+              hintText: 'Search by name or tag...',
-              MaterialPageRoute(
+              prefixIcon: Icon(Icons.search),
-                builder: (context) => FormulaScreen(
+              border: OutlineInputBorder(),
-                  formula: formula,
+            ),
-                  corpus: corpus,
+          ),
-                ),
+        ),
-              ),
+        Expanded(
-            );
+          child: ListView.builder(
-          },
+            itemCount: _filteredFormulas.length,
-        );
+            itemBuilder: (context, index) {
-      },
+              final formula = _filteredFormulas[index];
+              return ListTile(
+                title: Text(formula.name),
+                subtitle: formula.tags.isNotEmpty 
+                    ? Text('Tags: ${formula.tags.join(', ')}')
+                    : null,
+                onTap: () {
+                  Navigator.push(
+                    context,
+                    MaterialPageRoute(
+                      builder: (context) => FormulaScreen(
+                        formula: formula,
+                        corpus: widget.corpus,
+                      ),
+                    ),
+                  );
+                },
+              );
+            },
+          ),
+        ),
+      ],
     );
   }
 }