Ignore Python bytecode; untrack two stale committed .pyc files

Adds __pycache__/ and *.pyc to the root .gitignore, and removes from
version control the two bytecode files that had been committed under
build-env/__pycache__/.

The repo had no ignore rule for bytecode anywhere except
MW4COMPARE/tools/.gitignore, which I added with the decompiler toolchain
and which only covers that subtree. So running any script under
build-env/ leaves an untracked .pyc behind; extract-mw4.cpython-312.pyc
appeared while the decompiler was reusing build-env/extract-mw4.py for
.mw4 container parsing.

Untracked:
  build-env/__pycache__/replay-mr.cpython-314.pyc
  build-env/__pycache__/variant-to-subsystems.cpython-314.pyc

These are generated artefacts, and the filename carries the interpreter
tag - both are cpython-314 while this machine runs 3.12, so they are
stale bytecode that no interpreter here will load and that will never be
refreshed in place. Removed with `git rm --cached`, so both files remain
on disk and simply stop being version-controlled; they regenerate on
import as needed.

Note a .gitignore rule does not affect already-tracked files, which is
why the explicit untracking was required in the same change.

Co-authored-by: Claude Opus 5 (Anthropic) <noreply@anthropic.com>
Co-authored-by: GitHub Copilot <copilot@github.com>

.gitignore

@@ -8,10 +8,10 @@
 #  state you decide you never want mirrored.)
 
 # run-firestorm skill screenshots (may capture the operator's desktop -- never mirror)
-.claude/skills/run-firestorm/shots/
+.claude/skills/run-firestorm/shots/
 
 # FS507D_20161015: later FireStorm release drop, kept local for analysis -- not part of the mirror
-FS507D_20161015/
+FS507D_20161015/
 
 # player-created mechlab variants in the game deploy (local test/play data, per-machine)
 MW4/Resource/Variants/
@@ -19,3 +19,7 @@ MW4/Resource/Variants/
 # GameOS run-time reports: rewritten on every launch, per-machine
 MW4/gos-displays.txt
 MW4/gos-fps.txt
+
+# Python bytecode cache: regenerated on import, and the filename is interpreter-specific
+__pycache__/
+*.pyc