chore: gitignore generated wallet key dumps and operator .bak backups

Keeps secret wallet dumps (*-wallet.json, e.g. supplier/.deepseek-wallet.json
which contains privateKeyHex) and hand-made .bak hotfix backups out of git so
operator boxes stay clean. None of these were ever tracked.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitignore

@@ -18,6 +18,14 @@ data/
 # wallet-monitor: the real wallet list holds production mainnet addresses —
 # keep it out of git; only wallets.example.json is committed.
 wallet-monitor/wallets.json
+
+# Generated wallet key dumps (e.g. tx:gen-keypair output, supplier/.deepseek-wallet.json)
+# — these contain privateKeyHex. Never commit.
+*-wallet.json
+
+# Operator local file backups (e.g. docker-compose.buyer.yml.bak-20260609)
+*.bak
+*.bak-*
 .vitest-cache
 .DS_Store