RTBH/lab follow-up fixes: upgrade self-heal + pidfile identity

[vxfemboy]

Closes #80, closes #81 — two small, correct fixes from the C1c review backlog.

• RTBH: mirror self-heal misses the Auto->Manual upgrade journal write #80 — RTBH mirror self-heal covers the Auto→Manual upgrade. The upgrade path in RtbhManager::apply_add logged a journal-write failure without queuing a retry, leaving the mirror row's origin stale (auto) after a transient DB blip. It now routes the failure through queue_mirror(Announce { origin: Manual }), so the next tick heals it as Manual. Regression-tested (manual_upgrade_journal_failure_self_heals_as_manual).
• lab: kill_pidfiles should verify process identity (PID-reuse race) #81 — lab kill_pidfiles verifies process identity. Teardown now reads /proc/<pid>/comm and only SIGKILLs if it's bird, so a recycled/dead PID is skipped (PID-reuse race).

The two larger backlog items — #79 (BGP session-task supervision) and #82 (BGP transport security, TCP-MD5/GTSM) — remain tracked for later.

Verified: DATABASE_URL=… cargo test --workspace, cargo fmt --all --check, cargo clippy --workspace --all-targets -- --deny warnings, bash scripts/coverage.sh all green.

🤖 Generated with Claude Code