feat(debug): enable Python debug workflow and debug server integration

Adds an end-to-end Python debug workflow for the extension.
Includes a new prepare-debug.ps1 script and a VS Code task.
Extends the Python server and extension to coordinate a debug session and safe startup.

- Add prepare-debug.ps1 and a VS Code task to build the debug bundle
- Enable Python debug wiring in the server and tests
- Ensure a single stable Python debug session during startup

server/tests/python_tests/test_debug_server.py

@@ -0,0 +1,53 @@
+import sys
+from pathlib import Path
+
+import pytest
+
+
+THIS_DIR = Path(__file__).parent
+SRC_DIR = THIS_DIR.parent.parent / "src"
+if str(SRC_DIR) not in sys.path:
+    sys.path.insert(0, str(SRC_DIR))
+
+import _debug_server
+
+
+def test_debug_endpoint_defaults(monkeypatch):
+    monkeypatch.delenv("NXPS_DEBUG_HOST", raising=False)
+    monkeypatch.delenv("NXPS_DEBUG_PORT", raising=False)
+
+    assert _debug_server._debug_endpoint() == ("127.0.0.1", 5678)
+
+
+@pytest.mark.parametrize("port", ["invalid", "0", "65536"])
+def test_debug_endpoint_rejects_invalid_port(monkeypatch, port):
+    monkeypatch.setenv("NXPS_DEBUG_PORT", port)
+
+    with pytest.raises(RuntimeError):
+        _debug_server._debug_endpoint()
+
+
+def test_connect_debugger_retries_until_adapter_is_ready(monkeypatch):
+    class FakeDebugpy:
+        def __init__(self):
+            self.connect_calls = 0
+            self.wait_calls = 0
+
+        def connect(self, endpoint):
+            assert endpoint == ("127.0.0.1", 5678)
+            self.connect_calls += 1
+            if self.connect_calls < 3:
+                raise ConnectionRefusedError("listener is starting")
+
+        def wait_for_client(self):
+            self.wait_calls += 1
+
+    fake_debugpy = FakeDebugpy()
+    monkeypatch.setattr(_debug_server.time, "sleep", lambda _seconds: None)
+
+    _debug_server._connect_debugger(
+        fake_debugpy, "127.0.0.1", 5678, timeout=1.0
+    )
+
+    assert fake_debugpy.connect_calls == 3
+    assert fake_debugpy.wait_calls == 1