feat(sync): implement state-based bootstrap detection to resolve genesis deadlock

Resolves critical issue preventing network initialization from genesis state.

Problem:
- Nodes at height 0 with no peers remained in DiscoveringPeers state indefinitely
- Block production rejected with NotSynced error during peer discovery
- Two-node regtest networks could never bootstrap from genesis
- Created permanent deadlock preventing any block production

Solution:
- Implement multi-factor bootstrap detection with 30-second timeout
- Allow block production when: height==0 AND no_peers AND timeout_reached
- Add state transition tracking to accumulate discovery time
- Reset bootstrap timer when first peers are discovered
- Prevent fork creation by restricting bootstrap to genesis (height==0) only

Key Changes:
- Add bootstrap timing fields to SyncActor (state_entered_at, discovery_time_accumulated)
- Implement transition_to_state() helper with automatic time tracking
- Implement determine_sync_state() with bootstrap detection logic
- Implement check_bootstrap_mode() with multi-factor safety checks
- Update get_sync_status() to use new bootstrap-aware logic
- Update UpdatePeers handler to reset timer on peer discovery
- Refactor all state transitions to use timing-aware helper method

Safety Features:
- Genesis-only restriction prevents forks during network partitions
- Multi-factor detection prevents false positives
- Self-correcting: automatically exits bootstrap when peers appear
- Progressive logging (trace -> info -> warn) for operational visibility

Testing:
- 8 comprehensive unit tests covering all bootstrap scenarios
- Tests validate fork prevention (height > 0 blocked)
- Tests verify timer accumulation and reset logic
- All tests passing with 100% success rate

Documentation:
- SYNC_BOOTSTRAP_IMPLEMENTATION_PLAN.md provides complete technical analysis
- Inline documentation explains bootstrap detection logic
- Implementation plan includes regtest testing procedures

Author: michaelgpt