delivery-log-storage: agreed, plan and checklist

The owner agreed the item on 2026-10-12 (option 1 of the roadmap entry: store
the lines). plans/delivery-log-storage.md records what that means in detail:
every mail.log line headed by a queue id goes into send_log_lines with the
line's own time; a line is a row's when the id matches and its time lies
within the row's queue lifetime, which is the bound against Postfix reusing
ids; a line whose id has no send-log row is deleted after an hour, which is
both the retention and the clean-up of inbound and bounce lines; the page
reads the table and falls back to the current file for rows older than it.
Eight checklist steps, cut 2.2.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/development.md

@@ -126,6 +126,7 @@ than the default «meaningful step» rule in [§ Commits and release build](#com
 | 13 | panel-redesign | `2.0.0` (MAJOR, no compatibility) |
 | 14 | DMARC ingest drops and bounds, full backup from the panel, no queue in a backup | `2.0.1` (PATCH) |
 | 15 | inbound-antispam-panel | `2.1.0` (was `1.10.0`, reordered 2026-10-09) |
+| 16 | delivery-log-storage | `2.2.0` |
 
 Docs-only prep (checklists in plans, no product code) uses the same per-step
 commit rule but **no** version cut until the next product stage ships.