Omit invalid completed reasoning durations

[bb-slop-cop]

Human comments

What was wrong

Daemon event batches can give reasoning start and completion rows the same persisted timestamp. The completed-reasoning projection always formatted their difference as elapsed time, so unavailable timing data became a false zero-duration title. The verified reproduction and root-cause report is https://get-bb.github.io/reports/issues/3219.html.

What changed

Completed reasoning now includes a duration only when completion is later than start. Equal or reversed timestamps render the neutral Thought title, while truthful positive durations keep the existing Thought for <duration> form.

The change is contained to @bb/thread-view. It does not change the host-daemon protocol, persisted events, CLI contract, Plugin SDK, configuration, migrations, generated files, or dependencies.

How you verified

• The focused regression failed on unchanged origin/main: expected Thought, received Thought for 0ms.
• The same failure reproduced in a second clean checkout at 06aeaa994942ae7527dc49d2268c1f801e8542a0.
• After the fix, the focused regression passed.
• pnpm exec turbo run test typecheck --filter=@bb/thread-view passed: 379 tests and typecheck.
• git diff --check origin/main passed.
• git diff --numstat origin/main reports 57 changed text lines across 2 files (54 additions, 3 deletions) and no binary changes.

Fixes #3219

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