Related to #637
The sensor-proxy was failing to start on systems with read-only filesystems
because audit logging required a writable /var/log/pulse/sensor-proxy directory.
Changes:
- Modified newAuditLogger() to automatically fall back to stderr (systemd journal)
if the audit log file cannot be opened
- Removed error return from newAuditLogger() since it now always succeeds
- Added warning logs when fallback mode is used to alert operators
- Updated tests to handle the new signature
- Added better debugging to audit log tests
This allows the sensor-proxy to run on:
- Immutable/read-only root filesystems
- Hardened systems with restricted /var mounts
- Containerized environments with limited write access
Audit events are still captured via systemd journal when file logging is
unavailable, maintaining the security audit trail.
