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/CentralUI/findings.md

@@ -8,7 +8,7 @@
 | Last reviewed | 2026-05-28 |
 | Reviewer | claude-agent |
 | Commit reviewed | `1eb6e97` |
-| Open findings | 4 |
+| Open findings | 3 |
 
 ## Summary
 
@@ -1498,9 +1498,11 @@ the expected line count regardless of thread interleaving.
 |--|--|
 | Severity | Low |
 | Category | Performance & resource management |
-| Status | Open |
+| Status | Resolved |
 | Location | `src/ScadaLink.CentralUI/Components/Pages/Design/TransportImport.razor.cs:72,104-142,160-161` |
 
+**Resolution (2026-05-28):** Replaced the `private byte[]? _bundleBytes` field with `private string? _bundleTempPath`. `OnFileSelectedAsync` now creates `Path.GetTempPath()/scadalink-transport-staging/` (created on first use) and streams the upload via `InputFile.OpenReadStream(maxBytes).CopyToAsync(FileStream)` straight to a `Guid.NewGuid():N + .scadabundle` temp file; `TryLoadAsync` opens the same path as a fresh `FileStream` for each `IBundleImporter.LoadAsync` call. The component now implements `IDisposable` and a `DeleteBundleTempFile()` helper that runs on `ResetSessionState`, `OnFileSelectedAsync` (before a new upload), and `Dispose` (circuit teardown); IO failures during cleanup are swallowed so audit-failure-style defensive semantics hold. Per-circuit working set drops from up to `MaxBundleSizeMb` (default 100 MB) per open wizard to the 80 KB FileStream buffer. The existing reflection-based test helper `SeedAtPassphraseStep` was migrated to write bytes to a real temp file and set `_bundleTempPath`, so the 7 existing TransportImport bUnit tests still pass against the new staging model.
+
 **Description**
 
 `OnFileSelectedAsync` reads the uploaded `.scadabundle` into a `MemoryStream`,