Derive the version from git with verri

Use verri's strawberry flavour through hatchling's code version source, so
versions look like 2026.10.21.0: the HEAD commit date plus the number of
earlier commits that day.

Container images build the sdist in a separate stage that has the git
repository, so they get the same version instead of a +vcs.missing one.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.containerignore

@@ -1,8 +1,6 @@
-.git
 **/__pycache__
 **/*.pyc
 .venv
-tests
 **/build
 **/dist
 **/*.egg-info