delete: verify the host-data wipe before printing ✔ (RFC-0003 offboard hygiene)

[saadqbal]

tracebloc delete prints ✔ Removed local tracebloc data and config after removeHostDataDir() (os.RemoveAll(config.Dir())) returns nil — but a nil RemoveAll is not proof the tree is gone (racing writer, mount, masked partial failure). Claiming a clean wipe we didn't achieve is exactly the offboard-hygiene gap RFC-0003 flags (§2.4 / §3.3).

Fix: after RemoveAll, stat the dir; treat "still present" (or an unexpected stat error) as a failure so the caller prints the warn + manual-rm hint instead of ✔. Added an osStat seam + a test proving delete does NOT claim success on an unverified wipe.

The cli-side follow-up from tracebloc/client#367 (RFC-0003 Option C). Under node-local the heavy multi-path wipe is unnecessary; this is the honesty fix that stands regardless. Design: backend#1151. RFC: #366.

[LukasWodka]

Closing as completed — the implementing PR merged; only the issue never closed.

Why it stayed open: this repo's default branch was main while the PR merged to develop, and GitHub fires closing keywords only on merges into the default branch. So Closes #N never triggered here, no matter how it was written.

Fixed at the source today (2026-07-25): this repo's default branch is now develop, so closing keywords will work from here on. The PR template was also corrected — it previously suggested Ref tracebloc/other-repo#456 for cross-repo links, and Ref is not a closing keyword.

Closed as part of a board hygiene pass. If any part of this issue is not actually covered by the merged PR, please reopen — it was closed on the strength of a merged reference, not a line-by-line audit.