chore: enhance security configuration across applications

- Add root-level *.json to .gitignore to prevent wallet backup leaks
- Replace wildcard CORS origins with explicit localhost URLs across all apps
- Add OPTIONS method to CORS allowed methods for preflight requests
- Update coordinator database to use absolute path in data/ directory to prevent duplicates
- Add JWT secret validation in coordinator config (must be set via environment)
- Replace deprecated get_session dependency with Session

.gitignore

@@ -150,6 +150,9 @@ home/client/client_wallet.json
 home/genesis_wallet.json
 home/miner/miner_wallet.json
 
+# Root-level wallet backups (contain private keys)
+*.json
+
 # ===================
 # Stale source copies
 # ===================