[03-Developer] #260 in-app tool calling (Gemma 4 multi-turn)

ADR-0005 in-process tool runtime — 6 tools (catalog 2 + tracker 2 +
habit 2), ToolDispatcher with JSON-schema validation + modal ConfirmGate
for destructive ops, multi-turn LlmChatSession abstraction wired to
flutter_gemma 0.16.5 (ToolChoice.auto), ChatSessionController with
MAX_TURNS=4 safety + 8-turn history hint, ChatScreen entry behind AI
opt-in. R3/R7/R8 enforced inside handlers. 41 new tests (envelope,
catalog/tracker/habit tools, dispatcher, controller loop) — 151 total
passing.

Refs #260

app/lib/main.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 
+import 'ai/tools/tool_definition.dart' as tools;
 import 'data/ai/gemma_llm_service.dart';
 import 'data/ai/llm_service.dart';
 import 'data/ai/model_lifecycle.dart';
@@ -77,6 +78,12 @@ class _LazyLlmService implements LlmService {
     Map<String, dynamic> schema,
   ) async =>
       (await _resolve()).generateStructured(prompt, schema);
+
+  @override
+  Future<LlmChatSession> startChat({
+    required List<tools.ToolDefinition> tools,
+  }) async =>
+      (await _resolve()).startChat(tools: tools);
 }
 
 class LifeHelperApp extends StatelessWidget {