T-127: replace InProcessClient with socket loopback

Fourth slice of T-99. The UI's DaemonClient now talks to its own
IpcServer through the same per-workspace Unix socket the C `clide`
client uses — one transport, one wire contract, no second path
through the dispatch tree.

Changes:
* lib/kernel/src/ipc/in_process.dart deleted. Nothing imports it.
* DaemonClient.socketPath becomes mutable + new `reconnectAt(path)`
  method swaps an active client onto a different socket without
  restart. Project switch in main.dart uses it — the dispatcher
  + IpcServer are rebuilt for the new workspace, and the client
  reconnects to the new path.
* main.dart's daemonClientFactory now builds a real DaemonClient
  pointed at workspaceSocketPath(workRoot); swapIpcServer kicks
  off server.start() then client.start() in sequence.
* lib/test_app.dart's pane.spawn smoke test uses dispatcher.dispatch
  directly instead of InProcessClient — same coverage, no dead-end
  import.
* DaemonClient client_test gets a reconnectAt round-trip test.

T-128 (delete IsolateClient + Backend + backend_entry.dart) unblocked.

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

test/kernel/src/ipc/client_test.dart

@@ -276,5 +276,45 @@ void main() {
       await Future<void>.delayed(const Duration(milliseconds: 100));
       expect(flips, contains(true));
     });
+
+    test('reconnectAt swaps socket paths and re-binds (T-127)', () async {
+      final pathA = await _tmpSocket();
+      final daemonA = _TestDaemon(pathA);
+      await daemonA.start();
+      addTearDown(daemonA.close);
+
+      final bus = DaemonBus();
+      addTearDown(bus.dispose);
+      final client = _build(pathA, bus);
+      addTearDown(client.dispose);
+      await client.start();
+      await daemonA.waitForClient();
+      await Future<void>.delayed(const Duration(milliseconds: 50));
+      expect(client.isConnected, isTrue);
+      expect(client.socketPath, pathA);
+
+      // Spin up a SECOND daemon on a different socket and move the
+      // client over to it.
+      final pathB = await _tmpSocket();
+      final daemonB = _TestDaemon(pathB);
+      await daemonB.start();
+      addTearDown(daemonB.close);
+
+      await client.reconnectAt(pathB);
+      await daemonB.waitForClient();
+      await Future<void>.delayed(const Duration(milliseconds: 50));
+      expect(client.socketPath, pathB);
+      expect(client.isConnected, isTrue);
+
+      // A request goes to the NEW daemon — verify by reading the
+      // line off daemonB.lines.
+      final lineFuture = daemonB.lines.first;
+      final responseFuture = client.request('ping');
+      final reqLine = await lineFuture;
+      final reqJson = jsonDecode(reqLine) as Map<String, Object?>;
+      daemonB.send(IpcResponse.ok(id: reqJson['id'] as String, data: const {'pong': true}).encode());
+      final resp = await responseFuture;
+      expect(resp.ok, isTrue);
+    });
   });
 }