audit 3: every per-message question of the send log has its index

Migration 0010 (DDL only; 0009 went to stage 2b). EXPLAIN QUERY PLAN of
every send_log statement showed, beyond M2 as written (stage 2 had already
moved the by-domain counts onto (domain_id, created_at)):

- the tailer's sweep of open rows (every 5 min) and its count scanned the
  table: partial idx_send_log_open (created_at) WHERE status IN ('queued',
  'deferred'), the statuses literal in the statements, ORDER BY +id (else
  SQLite walks the table in id order to skip a sort);
- AttachRefusalLine's NOT EXISTS (... refusal_line = ?1) scanned the table
  for every refusal line: partial idx_send_log_refusal_line, the query
  carrying the index's WHERE; its row found by idx_send_log_rejected
  (status literal, +queue_id) instead of every refusal without a queue id;
- an application's level-2 count went through its domain's index:
  +domain_id in appByLogin;
- a page of one domain's or one application's log sorted all of it:
  idx_send_log_domain_id, idx_send_log_app_login (id order; several domains
  still sort, top-N). idx_send_log_domain stays for the global filter.

The statements are constants and builders (countMessagesQuery,
peakPerHourQuery, listOpenQuery, countOpenQuery, sendLogPageQuery,
attachRefusalLineQuery, limitRefusalsQuery) and
TestSendLogQueriesUseTheirIndexes explains exactly those: the index each
must use, no SCAN of send_log, no sort where none is wanted; the literal
statuses checked against the constants. It replaces the hand-written plan
check of TestLimitRefusalsSince.

Tested on the test server: go vet + go test of 24 packages, make e2e (all
pass) on this tree.

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

CHANGELOG.md

@@ -5,8 +5,20 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ## [Unreleased]
 
+Migration `0010` (indexes only).
+
 ### Fixed
 
+- **Questions asked of the send log on every message or every few minutes
+  walked the whole table.** Measured with SQLite's own plans against the
+  statements the panel runs: the sweep for rows still queued or deferred
+  (every 5 minutes) and the check whether a refusal line from `mail.log` is
+  already on a row (every such line) read every row of the retention
+  period; a level-2 limit of an application counted through all of its
+  domain's rows; a page of a domain administrator's log sorted the domain's
+  whole log. Migration `0010` adds four indexes, and a test now holds each
+  of these statements to its index (audit 2026-10-12, M2).
+
 - **A restore whose first start failed never ran its Resync.** The panel
   removed the restore manifest as soon as it had checked the version, before
   it opened the database and regenerated the mail maps from it; a start that