Add fault management to ros2_medkit: fault reporting with two-level filtering
(local + central), persistent storage, lifecycle management, and REST API access.

Goals:

• Two-level filtering: FaultReporter (local) + FaultManager (central)
• Multi-source fault aggregation by fault_code
• Persistent storage
• REST API and SSE for monitoring
• Backwards compatibility with diagnostic_updater

Success Criteria:

• FaultReporter library with local filtering (default enabled)
• FaultManager with central aggregation and lifecycle
• Storage survives restarts
• REST API + SSE working