installer: find userData by package name too, delete long paths; recover a half-removed env

[CSSFrancis]

Three bugs found by running Ground Crew's real NSIS installer (directelectron/de_ground_crew#542). Two are in installer.nsh, which had never been run, and one is in pythonEnv.

1. The uninstaller and the update sweep looked in the wrong userData folder

Electron names userData after package.json's productName, and falls back to its name. GC sets productName only in electron-builder.yml, so its userData is %APPDATA%\de-groundcrew. installer.nsh used ${APP_FILENAME}, which is Ground Crew. As a result:

• the uninstaller never offered to remove the Python environment;
• the install/update sweep could not see a stray sidecar (its python-env / python processes).

Both now check ${APP_PACKAGE_NAME} and ${PRODUCT_NAME}. Both belong to the app, so a sibling app's data is still out of reach.

2. "Yes, remove it" left files behind

NSIS's RMDir /r stops at MAX_PATH. jupyterlab-widgets puts 330-character paths in the env and in the uv cache, so 17 files (3.5 MB) survived. The macro now runs rd /s /q "\?\…" first, and RMDir catches anything left.

3. A half-removed env bricked the next install

What #2 left behind is a python-env with no pyvenv.cfg. uv refuses that directory ("cannot be used because it is not a valid Python environment"), so after a reinstall GC sat on the env-setup error on every launch. resolvePythonEnv now clears such a directory before setup (clearBrokenEnv). The directory is the shell's own. The same state can also come from a crash mid-delete.

Tested (Windows, GC installer built against this branch, NVIDIA GPU)

• Recovery: installed over the app stuck on the broken env. The installer closed it; on relaunch the leftover was cleared and the GPU env rebuilt online in 163 s.
• Uninstall answering Yes, with the app running: the prompt appeared; all 8 app and sidecar processes were closed; python-env, uv-cache, python, requirements.offline.txt and wheelhouse were all removed; settings, logs and Chromium data were kept.
• Also re-checked on this build: silent install; reinstall over a running app (env untouched); silent uninstall (env kept, the /SD IDNO default).
• Unit tests: clearBrokenEnv against a past-MAX_PATH leftover, a real venv and a missing dir. 175 pass, and the typecheck is clean.