Add CHANGELOG; require an explicit release TAG

Adding a game is a minor bump, so the collection is at v1.2.0: v1.0.0 shipped
GB4, Burglin' Gnomes was a minor bump that was never cut, and Expedition 33 is
the second. Skipping the unreleased 1.1.0 reflects the real history better than
collapsing two games' worth of additions into one bump.

publish.sh no longer defaults TAG to v1.0.0, which could silently re-cut the
existing release; it now requires TAG explicitly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tools/publish.sh

@@ -17,7 +17,7 @@ GAME="${GAME:-all}"
 if [ "$GAME" = "all" ]; then
   GAME=$(for d in games/*/; do [ -f "$d/game.conf" ] && basename "$d"; done | tr '\n' ' ')
 fi
-TAG="${TAG:-v1.0.0}"
+TAG="${TAG:?set TAG explicitly, e.g. TAG=v1.2.0 (see CHANGELOG.md)}"
 # Single game -> its own README; multiple -> the collection README.
 if [ "$(echo "$GAME" | wc -w)" -eq 1 ] && [ -f "games/$GAME/README.md" ]; then
   NOTES="${NOTES:-games/$GAME/README.md}"