fix(ingest): recover WAL segments shipped at shutdown - #1213

🟢 Confidence 4/5 · likely safe to merge
_{quality 100/100 · no findings · tests covered · risk high}

Adds a retired/ owner marker so shutdown-shipped WAL segments are claimable at any age, makes a sealed segment count as exported when the cursor sits at its end, and keeps an owner claimable while recovery leaves segments behind. The logic reads correctly and is covered by new tests.

• retire() writes retired/<owner> before dropping the heartbeat; stale_owners lists it
• WalLane::is_behind lets a cursor parked at a sealed segment's end count as exported
• recover_orphans keeps the owner claimable when segments are left behind

_{ea5f8ef · Updated on every push. Reply "won't fix" to dismiss a finding, or mention @maple-review-bot to ask about one.}