Combat rework: packs, abilities, rest, health potions, group bosses

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

flake.nix

@@ -27,7 +27,7 @@
             chmod -R u+w source
             cd source
             python3 -m unittest discover -s tests -v
-            python3 -m py_compile app.py game.py
+            python3 -m py_compile app.py game.py combat.py
             node --check static/app.js
             touch $out
           '';