Harden Decodex power-loss recovery

[yvette-carlisle]

Summary

• add boot + process-start identity checks to Decodex run activity markers
• expose process_liveness_reason in status/dashboard/agent evidence
• add retry recovery prompt context and kill/PID-reuse/previous-boot regression coverage

Validation

• cargo make fmt-check
• cargo make check-rust
• cargo test -p decodex run_project_once_retries_recovered_worktree_after_marker_process_is_killed -- --nocapture
• cargo test -p decodex run_project_once_retries_recovered_worktree
• cargo test -p decodex operator_status_snapshot_counts_reused_pid_as_attention_not_running
• cargo test -p decodex operator_status_snapshot_counts_previous_boot_process_as_attention_not_running
• cargo test -p decodex --lib -- --test-threads=1