feat(cockpit): retire PySide6/PyInstaller — remove the LGPL artifact ahead of the web-app rebuild (#355)

[dngioidev]

Closes #355 — parent epic #350 (Cockpit v2, ADR-0008).

Per the owner's 2026-08-03 decision, remove the PySide6 (LGPLv3) desktop UI and PyInstaller packaging now, ahead of web-app parity, so the license check is clean with zero exceptions before the OSS/MIT flip. The framework-agnostic Python cores are retained; the FastAPI web app (#351) rebuilds the UI on them. No runnable desktop cockpit UI in the interim.

Acceptance criteria

• AC.1 — PySide6, pywinpty, PyInstaller, pytest-qt removed from pyproject.toml; uv.lock regenerated; forge-cockpit.spec deleted. Cores + psutil (+ pytest) kept. The forge-cockpit entry point (target deleted) was removed; package relicensed MIT.
• AC.2 — Qt presentation layer deleted (app.py, __main__.py, terminal.py, *_view.py); no remaining module imports PySide6/pywinpty; __init__.py stripped to a cores-only package init. Cores import cleanly; the six core test suites pass.
• AC.3 — the PySide6 LGPL exception removed from license.mjs (PYTHON_LICENSE_EXCEPTIONS now empty; pyside6/pywinpty/pytest-qt dropped from the SPDX map). #349 tests updated to assert no non-permissive Python license and no lingering exception.
• AC.4 — cockpit-python CI job is now cores-only (no Qt/offscreen env); license job green with zero exceptions; pnpm verify green.
• AC.5 — ADR-0006 Decision 1 + ADR-0008 note PySide6 removed ahead of parity (UI absent until Cockpit v2: localhost backend — serve the Python cores over 127.0.0.1 #351); tools/runner-ui/README + runner-adoption guide + docs route index reflect the cores-only interim; docsync gate green.

Test deviation from the ticket inventory (honest note)

The ticket's KEEP list included tests/test_fleet_control.py, but on inspection it imports FleetTab from fleet_view and LogViewer from log_view (both deleted Qt modules) and uses the qapp/qtbot pytest-qt fixtures. Per the ticket's own "verify each test's imports before deciding" instruction, it is a Qt UI test and was deleted alongside the other Qt suites. The six genuinely framework-agnostic core suites are kept.

Verification (this branch)

• license gate — node plugin/scripts/gates/license.mjs:
  license: clean — plugin declares MIT; all npm dependency licenses within the allowlist (9 ids); 2 Python dep(s), 0 documented exception(s) — exit 0, zero exceptions.
• pytest (cores-only, fresh venv from the committed uv.lock) — uv sync --frozen + uv run --frozen pytest -q: 106 passed (no Qt, no offscreen).
• pnpm verify — vitest: 58 files / 675 passed.
• docsync gate — doc-sync: clean (54 docs indexed).
• Repo-wide grep confirms no remaining PySide6/pywinpty/pytest-qt/forge-cockpit.spec/entry-point references in code, CI, or gitignore (only historical CHANGELOG/spike entries remain, intentionally).

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