Slim PyTAG jar + release automation

[martinballa]

Summary

• Adds a second maven-assembly-plugin execution producing target/TAG-pytag.jar (~13MB vs ~404MB for the full TAG.jar), built from src/assembly/pytag-jar.xml. It keeps the core engine, all games, built-in players, and the Swing GUI/replay path, but excludes the Spark/Hadoop ML-learner, tablesaw analytics, and langchain4j/google-cloud dependency trees that PyTAG never touches. Verified end-to-end against the real PyTAG package via JPype (vector + JSON obs examples, multi-agent).
• Fixes a crash (NoSuchElementException) in SSPPlayerView, SGPlayerView, and GoFishPlayerView when constructing the GUI with no human player (e.g. all-AI games, or PyTAG's RL agents) - they called human.stream().toList().getFirst() instead of falling back to -1 like LoveLetterPlayerView already does. Found while sweeping games to verify the slim jar renders correctly.
• Adds .github/workflows/release-pytag-jar.yml: on publishing a GitHub release, builds the project and uploads target/TAG-pytag.jar as an asset named TAG.jar, matching the URL shape (.../releases/latest/download/TAG.jar) PyTAG's jar_setup.py expects.

Test plan

• mvn package builds both TAG.jar and TAG-pytag.jar cleanly
• TAG-pytag.jar verified against a real pip install -e . PyTAG checkout (JPype), running pt-action-masking.py (vector obs, action masking) and ma-random.py (JSON obs, multi-agent) to completion
• Swept ~11 games (incl. asset-heavy ones: Pandemic, ColtExpress, Dominion, Uno, Catan) launching the GUI manager on the slim jar with no exceptions
• Release workflow itself is untested against a real GitHub release (needs a maintainer to publish a release to trigger it)