chore: gitignore secrets, pycache, and adversarial-review artifacts

Add patterns for *secret* files (e.g. operator-saved HMAC secrets at
repo root), __pycache__/ directories, and .adversarial-review/ run
artifacts so they don't get accidentally committed via 'git add -A'.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,6 +1,9 @@
 .worktrees/
 .agent/
 .claude/
+.adversarial-review/
 graphify-out/
 firmware/.pio/
 *.log
+*secret*
+__pycache__/