v3.2.6-sr94.19.2: safe concurrent expiry editing

Fix: stale expiry cannot silently return

• Unrelated personal/admin edits no longer resubmit an unchanged relative expiry or extend it from the current time.
• Explicit stale expiry changes and removals conflict atomically, keep the user's draft and show the current expiry for a deliberate retry.
• Independent availability and target/description drafts are preserved. Expiry removal is always accessible and resets after success.
• Admin validation responses keep the correct editor route; trailing admin table trigger syntax errors are removed, and edit errors wrap on mobile.
• Added API, fragment and native desktop/mobile browser regressions. JSON API behavior and database schema are unchanged.

Reload an editor opened before upgrading before saving a nonempty relative duration. Preserve the existing JWT secret and follow the verified backup/restore/deployment instructions in docs/DEPLOYMENT.md.

This is the first UI/UX remediation release, not completion of the full ledger. Remaining findings and user-assisted acceptance gates stay tracked in docs/UI-UX-REVIEW.md.