Restore completed review duration semantics in the sidebar

[lynnswap]

Parent: #96

Confirmed failure

v0.6.2 displayed an active timer from startedAt and froze it at endedAt, so a completed review showed its duration.

Current ReviewMonitor instead maps a completed ReviewRunRecord.endedAt to .relative(to: endedAt) and renders Text(date, style: .relative). The current test suite explicitly expects this age-since-completion behavior. Persisted rows without a live run fall back again to generic chat activity time and also lose review status/symbol.

Broken invariant

Review timing is lifecycle state owned by the review run. A completed review's visible time is endedAt - startedAt, not wall-clock age since endedAt and not generic thread recency.

Acceptance criteria

• Running reviews show elapsed time from their review start.
• Completed, failed, and cancelled reviews show a stable review duration based on lifecycle start/end.
• The displayed value does not change as wall-clock time advances after completion.
• Replay/restart either reconstructs the authoritative lifecycle timing or explicitly omits unavailable timing; it must not relabel thread age as review duration.
• Review status, symbol, target title, and timing come from one semantic review projection.
• Tests use an injected/fixed clock and cover live completion, persisted replay, cancellation, failure, missing lifecycle metadata, and wall-clock advance.
• No formatter-only patch or fallback to activityDate is used to mask missing ownership.

Regression evidence

• 3799f6b first discarded runtime review timestamps from the row path.
• 8a820eb completed the generic chat migration.
• 0ff385f explicitly introduced .relative(to: endedAt) and its current test expectation.
• v0.6.2 ReviewMonitorJobRowView.TimerLabelView used a paused timer interval from start to end.