inspect: clearer end-of-run trail confirmation (posted+link / nothing to report)

When a trail-output run finishes, it now confirms one of:

• posted: the hook prints 'Posted the review verdict to trail #N as a finding.' + 'View the trail: <link>' (already in place), or
• nothing to report: 'Nothing to report, so nothing was posted to the trail.' (reworded from the vague 'no review output produced'), or
• unavailable / error: kept-local / 'Could not post ...' notices.

Local-mode and cancelled runs stay silent about the trail. Adds TestMaybePostReviewToTrail covering all branches (local silent, posted via hook, nothing-to-report skip+confirm, error surfaced, cancelled silent).