add Toolchain, GitClient, native directory picker

Toolchain centralizes binary resolution — replaces five ad-hoc
mechanisms (expandedPath, _resolveGit, _resolve, _resolvePtyc,
_existsOnPath). Resolves via Future.delayed after runApp to avoid
blocking the merged UI/platform thread on macOS.

GitClient wraps all git operations with a typed API. Every subprocess
call goes through _run() using toolchain.git + toolchain.gitEnv.
Replaces free functions in operations.dart.

Native directory picker: NSOpenPanel on macOS (method channel in
AppDelegate), GtkFileChooserDialog on Linux. Falls back to text-input
dialog on web or MissingPluginException. Shows "No git repo found"
dialog when the selected directory is not a git repository.

PqlClient and pane commands updated to use Toolchain. ToolCheck
replaced by Toolchain.missing/allOk. All IPC handlers now catch
GitException to prevent unhandled exceptions on the merged thread.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

test/daemon/git_commands_test.dart

@@ -1,6 +1,8 @@
 import 'dart:io';
 
 import 'package:clide/clide.dart';
+import 'package:clide/kernel/src/toolchain.dart';
+import 'package:clide/src/git/client.dart';
 import 'package:clide/src/daemon/git_commands.dart';
 import 'package:test/test.dart';
 
@@ -32,7 +34,10 @@ void main() {
 
     sink = RecordingEventSink();
     dispatcher = DaemonDispatcher();
-    registerGitCommands(dispatcher, sandbox, sink);
+    final toolchain = Toolchain();
+    toolchain.applyResolved(Toolchain.resolvePaths(workspaceRoot: sandbox.path));
+    final gitClient = GitClient(toolchain: toolchain, workDir: sandbox);
+    registerGitCommands(dispatcher, gitClient, sink);
   });
 
   tearDown(() async {

test/daemon/pane_commands_test.dart

@@ -9,6 +9,7 @@ import 'dart:convert';
 import 'dart:io';
 
 import 'package:clide/clide.dart';
+import 'package:clide/kernel/src/toolchain.dart';
 import 'package:clide/src/daemon/pane_commands.dart';
 import 'package:clide/src/panes/registry.dart';
 import 'package:test/test.dart';
@@ -16,9 +17,8 @@ import 'package:test/test.dart';
 void main() {
   if (!Platform.isLinux && !Platform.isMacOS) return;
 
-  final ptycPath = File('ptyc/bin/ptyc').existsSync()
-      ? File('ptyc/bin/ptyc').absolute.path
-      : 'ptyc';
+  final toolchain = Toolchain();
+  toolchain.applyResolved(Toolchain.resolvePaths(workspaceRoot: Directory.current.path));
 
   group('pane.* dispatch', () {
     late DaemonDispatcher dispatcher;
@@ -28,7 +28,7 @@ void main() {
       final sink = RecordingEventSink();
       registry = PaneRegistry(events: sink);
       dispatcher = DaemonDispatcher();
-      registerPaneCommands(dispatcher, registry);
+      registerPaneCommands(dispatcher, registry, toolchain: toolchain);
     });
 
     tearDown(() => registry.shutdown());
@@ -48,7 +48,7 @@ void main() {
       final r = await call('pane.spawn', {
         'argv': const ['/bin/sh', '-c', 'sleep 0.1'],
         'kind': 'terminal',
-        'ptyc_path': ptycPath,
+        'ptyc_path': toolchain.ptyc,
       });
       expect(r.ok, isTrue, reason: r.error?.message);
       expect(r.data['id'], startsWith('p_'));
@@ -58,12 +58,12 @@ void main() {
     test('pane.list shows spawned panes', () async {
       await call('pane.spawn', {
         'argv': const ['/bin/cat'],
-        'ptyc_path': ptycPath,
+        'ptyc_path': toolchain.ptyc,
       });
       await call('pane.spawn', {
         'argv': const ['/bin/cat'],
         'kind': 'claude',
-        'ptyc_path': ptycPath,
+        'ptyc_path': toolchain.ptyc,
       });
       final r = await call('pane.list', const {});
       final panes = (r.data['panes'] as List).cast<Map>();
@@ -74,7 +74,7 @@ void main() {
     test('pane.write accepts text or bytes_b64', () async {
       final spawn = await call('pane.spawn', {
         'argv': const ['/bin/cat'],
-        'ptyc_path': ptycPath,
+        'ptyc_path': toolchain.ptyc,
       });
       final id = spawn.data['id']! as String;
 
@@ -98,7 +98,7 @@ void main() {
     test('pane.resize + pane.close + pane.focus round-trip', () async {
       final spawn = await call('pane.spawn', {
         'argv': const ['/bin/cat'],
-        'ptyc_path': ptycPath,
+        'ptyc_path': toolchain.ptyc,
       });
       final id = spawn.data['id']! as String;
 

test/daemon/pql_commands_test.dart

@@ -1,6 +1,7 @@
 import 'dart:io';
 
 import 'package:clide/clide.dart';
+import 'package:clide/kernel/src/toolchain.dart';
 import 'package:clide/src/daemon/pql_commands.dart';
 import 'package:clide/src/pql/client.dart';
 import 'package:test/test.dart';
@@ -10,7 +11,9 @@ void main() {
   late PqlClient pql;
 
   setUp(() {
-    pql = PqlClient(workDir: Directory.current);
+    final toolchain = Toolchain();
+    toolchain.applyResolved(Toolchain.resolvePaths(workspaceRoot: Directory.current.path));
+    pql = PqlClient(workDir: Directory.current, toolchain: toolchain);
     dispatcher = DaemonDispatcher();
     registerPqlCommands(dispatcher, pql);
   });