Vendor debugpy for VS Code attach debugging

Bundles debugpy 1.7.0 directly in python/ so "Maya: Attach (debugpy)"
works with no per-machine pip install step. Installed via Maya 2022's
own pip so it resolved a version actually compatible with Python 3.7
(Maya 2022's interpreter), then verified import + listen() succeeds
under all three target Maya Python versions (3.7/3.9/3.10).

Also fixes a latent __file__-under-exec() bug in
start_debug_server.py (same pitfall as Maya's own plugin loader,
never hit until this exercised it) and corrects the README's Maya
Python version claim -- 2022 ships Python 3.7, not 3.9 as previously
stated, which was never independently verified until now.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

scripts/start_debug_server.py

@@ -1,12 +1,8 @@
 """Run this inside interactive Maya (Script Editor, Python tab) to enable
 the "Maya: Attach (debugpy)" launch config in .vscode/launch.json.
 
-One-time setup -- install debugpy into Maya's own Python environment
-(adjust the path for your Maya version):
-
-    "C:\\Program Files\\Autodesk\\Maya2024\\bin\\mayapy.exe" -m pip install debugpy
-
-Then, each Maya session, before attaching from VS Code:
+debugpy is bundled in ../python/ -- no separate pip install needed. Each
+Maya session, before attaching from VS Code, run:
 
     exec(open(r"C:\\workspace\\PoseRenderer\\scripts\\start_debug_server.py").read())
 
@@ -15,6 +11,16 @@ draw_override.py's prepareForDraw, or a command's doIt) will then pause in
 VS Code once you run "Maya: Attach (debugpy)".
 """
 
+import sys
+
+# Run via exec(open(path).read()) per the docstring above, so __file__ is
+# not defined here (same pitfall as Maya's own .py plugin loader) -- the
+# project's python/ dir is hardcoded to match where the exec() call above
+# already points. Adjust this if your checkout lives somewhere else.
+_PYTHON_DIR = r"C:\workspace\PoseRenderer\python"
+if _PYTHON_DIR not in sys.path:
+    sys.path.insert(0, _PYTHON_DIR)
+
 import debugpy
 
 _ALREADY_LISTENING_ATTR = "_openpose_renderer_debugpy_listening"