feat(swift-ios): show how long completed threads have been done - #7399

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Approvability

Verdict: Approved at e6270a0

Macroscope's review found this PR approvable — This is a localized iOS Home presentation change: completed rich rows use an existing completion timestamp for compact and accessibility-friendly elapsed ages, while invalid or missing data retains the existing fallback. It adds focused tests without changing schemas, workflows, defaults, infrastructure, or sensitive code.

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Updated after on-device review: the wording is gone.

Completed rows now show the bare elapsed time since completion — 15m, 2h 43m, 1d 2h — in the same slot and style as every other row's age label, instead of the earlier Done for <duration> sentence. Verdict from testing on device was simply "I just want how long since it was there".

What did not change is the substance of the feature: the age is still measured from latestTurnCompletedAt (when the task finished), not from last activity. A thread touched a minute ago but finished hours ago reads as hours, not as a minute.

Also in this update:

• Sub-minute completions read now, matching the existing age vocabulary rather than inventing a <1m form.
• VoiceOver keeps a full sentence and now substitutes it for the bare status word: "Completed 2 hours, 43 minutes ago" / "Completed just now".
• Threads with no completion timestamp still fall back to the last-activity age, unchanged.

Same four files, apps/swift-ios only. Focused suite T3CodeTests/HomeThreadMetadataTests: 13/13 passed, 0 failures on this head, and the tree was verified in the simulator — a fixture whose last activity was 9 minutes old but whose completion was 2h 44m old renders 2h 43m, confirming the label follows completion rather than activity.

Coordination trace: T3 thread 50F4FC2B-6485-41E5-80DA-BDCD2BE20428 · saphid/t3code-personal#119

Exact-head visual proof refreshed

Captured from PR head 6d7966cd75219e37c1ed98b48fb4b6530e30989e on the canonical proof simulator after installing the Debug app produced by the focused exact-head test build.

The completed Publish the migration guide row shows a multi-hour completion age even though its last activity was only minutes earlier; Sketch the settings redesign is the non-completed control row.

Light	Dark

• Focused tests: 13/13 passed, exit 0, ** TEST SUCCEEDED **.
• Light SHA-256: f2031e76b835c22b61ec0791de103824580bf2356c07b24a7ce3776c5fcd6ea2
• Dark SHA-256: e3d5b5df753c65d4ca2626aec188668f48e093170bd04c8c33f0b141d64e18a5
• Proof manifest

No video is needed because this change has no interaction or motion behavior.