Replace name-based bouncer validation with actual LAPI authentication
testing. The previous implementation checked if a bouncer NAME existed
but never validated if the API KEY was accepted by CrowdSec LAPI.
Key changes:
- Add testKeyAgainstLAPI() with real HTTP authentication against
/v1/decisions/stream endpoint
- Implement exponential backoff retry (500ms → 5s cap) for transient
connection errors while failing fast on 403 authentication failures
- Add mutex protection to prevent concurrent registration race conditions
- Use atomic file writes (temp → rename) for key persistence
- Mask API keys in all log output (CWE-312 compliance)
Breaking behavior: Invalid env var keys now auto-recover by registering
a new bouncer instead of failing silently with stale credentials.
Includes temporary acceptance of 7 Debian HIGH CVEs with documented
mitigation plan (Alpine migration in progress - issue #631).
0eb0660d41