refactor: drop packaging dependency, inline version parsing

The only user of 'packaging' was version_check.py — two small functions
(normalize_version, is_newer) that just need to parse "1.2.3-alpha.1"
and compare PEP 440-style versions. That's well within stdlib reach.

- Inline a NamedTuple-based Version with kind/pre_num ordering
  (dev < alpha < beta < rc < release), same regex-normalized format
- Define a local InvalidVersion exception
- Remove packaging>=23.0 from pyproject.toml dependencies

Why now: the Windows cross-build uses a hard-coded DEPS array in
build-dist-windows.sh, which was never updated when 'packaging' was
added on March 25. Result: importable from pip-installed dev envs,
missing from the portable installer — tray icon appeared but uvicorn
died with ModuleNotFoundError: No module named 'packaging'.

Removing the dep entirely is cleaner than adding one more hard-coded
entry to the Windows DEPS list. Tests (678 passing) and a manual test
matrix covering dev/alpha/beta/rc/release ordering all pass.

server/pyproject.toml

@@ -26,7 +26,6 @@ dependencies = [
     "fastapi>=0.115.0",
     "uvicorn[standard]>=0.32.0",
     "httpx>=0.27.2",
-    "packaging>=23.0",
     "mss>=9.0.2",
     "numpy>=2.1.3",
     "pydantic>=2.9.2",