perf: close Theme 6 — 11 allocation / N+1 / lock-contention findings

Well-localised perf fixes across 8 modules.

Lock decoupling / SQL streaming:
- AuditLog-005: SqliteAuditWriter gains dedicated read-only _readConnection
  (+ _readLock) backed by WAL journal mode. GetBacklogStatsAsync,
  ReadPendingAsync, ReadPendingSinceAsync, ReadForwardedAsync no longer
  contend with the hot-path INSERT lock — backlog probes on a 30s timer
  can't stall the writer under multi-hundred-K Pending backlog.
- SEL-022: dropped Cache=Shared from SiteEventLogger's default connection
  string (single-connection logger; mode was dormant config).

Memory / streaming:
- CLI-019: bundle export streams base64 in 1 MB-aligned chunks via
  Convert.TryFromBase64Chars straight into the FileStream — no more
  full-bundle byte[] allocation.
- CentralUI-031: TransportImport now stages the upload to a per-session
  temp file under Path.GetTempPath() (replaces in-memory byte[] field);
  page implements IDisposable to delete the temp file on reset / new
  upload / dispose. Per-circuit working set drops from ~100 MB to ~80 KB.

N+1 hoisting:
- Transport-008: added ITemplateEngineRepository.GetTemplatesWithChildrenAsync
  bulk method; BundleImporter.PreviewAsync calls it once instead of per-
  template-name. Single query with .Include(...).AsSplitQuery().
- DM-023: BuildDeployArtifactsCommandAsync's per-site loop now references
  a pre-fetched GlobalArtifactSnapshot (shared scripts, external systems,
  DB connections, notification lists, SMTP) instead of re-querying per site.
- MgmtSvc-023: HandleQueryDeployments unfiltered branch uses one
  GetAllInstancesAsync bulk load + Dictionary<int,int?> lookup (was a
  GetInstanceByIdAsync per record).

Small allocations / per-tick rebuilds:
- InboundAPI-019: AuditWriteMiddleware gates EnableBuffering() on
  RequestHasBody() so GET/HEAD/DELETE/TRACE/OPTIONS and Content-Length:0
  requests skip the FileBufferingReadStream allocation.
- NotifOutbox-006: ResolveAdapters dictionary now cached on
  _adaptersCache (built lazily on first sweep) + actor-lifetime
  _adaptersScope; ResolveAdapters no longer rebuilds per dispatch tick.

Verify-only:
- Comm-017: Confirmed _inProgressDeployments was deleted by Comm-016 in
  commit ac96b83 — marked Resolved with that attribution. No code change.

Doc-correction:
- NS-022: Updated MailKitSmtpClientWrapper XML doc to spell out single-
  connection / per-delivery-factory contract (option (b) — transient
  client per Send — rejected because it re-handshakes TLS per email).

10+ new regression tests across 8 test projects. Build clean; affected
suites all green. README regenerated: 54 open (was 65).

code-reviews/NotificationOutbox/findings.md

@@ -8,7 +8,7 @@
 | Last reviewed | 2026-05-28 |
 | Reviewer | claude-agent |
 | Commit reviewed | `1eb6e97` |
-| Open findings | 9 |
+| Open findings | 8 |
 
 ## Summary
 
@@ -279,7 +279,7 @@ remains the CD-015 raw-SQL `IF NOT EXISTS … INSERT` with `2601/2627` catch in
 |--|--|
 | Severity | Low |
 | Category | Performance & resource management |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.NotificationOutbox/NotificationOutboxActor.cs:267-277` |
 
 **Description**
@@ -310,9 +310,7 @@ sweeps") in the actor XML, or — preferred — cache only the *types* at startu
 (`PreStart`) and resolve the scoped instance per sweep, so future adapters with
 stateful intent (timeouts, circuit breakers) cannot accidentally lose state.
 
-**Resolution**
-
-_Unresolved._
+**Resolution (2026-05-28):** Cached the `NotificationType → adapter` dictionary on a new actor field `_adaptersCache`, built lazily on the first dispatch sweep that needs it. The cache is paired with an actor-lifetime `IServiceScope` (`_adaptersScope`, created on first use and disposed in `PostStop`) so the resolved scoped adapter instances live as long as the cache itself — respecting `EmailNotificationDeliveryAdapter`'s scoped lifetime without leaking captive-DbContext references across the actor's full lifetime. `RunDispatchPass` now calls `ResolveAdapters()` (instance method, no args), and the existing "resolved from the per-sweep scope" comment was rewritten to cross-reference the new cache rationale. Adapter set is static per process lifetime (confirmed against the DI registration in `AddNotificationOutbox`), so no invalidation hook is needed. Regression test `Dispatch_ResolvesAdaptersOnce_AcrossMultipleSweeps` registers a counting factory and pins the resolution count at exactly 1 across three end-to-end dispatch sweeps.
 
 ### NotificationOutbox-007 — `NotificationOutboxOptions.DispatchBatchSize`, `DeliveredKpiWindow`, and `PurgeInterval` are not in the design document