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).

tests/ScadaLink.ConfigurationDatabase.Tests/TemplateEngineRepositoryTests.cs

@@ -69,6 +69,66 @@ public class TemplateEngineRepositoryTests : IDisposable
         Assert.Null(loaded);
     }
 
+    [Fact]
+    public async Task GetTemplatesWithChildrenAsync_BulkVariant_FetchesEveryMatchingNameInOneQuery()
+    {
+        // Transport-008 regression: BundleImporter.PreviewAsync previously
+        // called GetTemplateWithChildrenAsync(stub.Id) per matching template
+        // name. The bulk variant returns every match in a single query.
+        var a = new Template("Alpha");
+        a.Attributes.Add(new TemplateAttribute("A1"));
+        a.Scripts.Add(new TemplateScript("AS1", "return 1;"));
+        var b = new Template("Beta");
+        b.Alarms.Add(new TemplateAlarm("BAlarm"));
+        var c = new Template("Gamma");
+        _context.Templates.AddRange(a, b, c);
+        await _context.SaveChangesAsync();
+
+        var result = await _repository.GetTemplatesWithChildrenAsync(new[] { "Alpha", "Beta", "DoesNotExist" });
+
+        Assert.Equal(2, result.Count);
+        var loadedA = Assert.Single(result, t => t.Name == "Alpha");
+        var loadedB = Assert.Single(result, t => t.Name == "Beta");
+        Assert.Single(loadedA.Attributes);
+        Assert.Equal("A1", loadedA.Attributes.First().Name);
+        Assert.Single(loadedA.Scripts);
+        Assert.Single(loadedB.Alarms);
+        Assert.Equal("BAlarm", loadedB.Alarms.First().Name);
+        Assert.DoesNotContain(result, t => t.Name == "Gamma");
+    }
+
+    [Fact]
+    public async Task GetTemplatesWithChildrenAsync_EmptyNames_ReturnsEmpty()
+    {
+        var result = await _repository.GetTemplatesWithChildrenAsync(Array.Empty<string>());
+
+        Assert.Empty(result);
+    }
+
+    [Fact]
+    public async Task GetTemplatesWithChildrenAsync_NullEnumerable_ReturnsEmpty()
+    {
+        var result = await _repository.GetTemplatesWithChildrenAsync(null!);
+
+        Assert.Empty(result);
+    }
+
+    [Fact]
+    public async Task GetTemplatesWithChildrenAsync_FiltersOutDuplicatesAndEmptyStrings()
+    {
+        var a = new Template("Alpha");
+        _context.Templates.Add(a);
+        await _context.SaveChangesAsync();
+
+        // Duplicate names + empty / null entries should not throw; the helper
+        // deduplicates and filters them out before the SQL IN clause.
+        var result = await _repository.GetTemplatesWithChildrenAsync(
+            new[] { "Alpha", "Alpha", "", null!, "Alpha" });
+
+        Assert.Single(result);
+        Assert.Equal("Alpha", result[0].Name);
+    }
+
     [Fact]
     public async Task GetTemplateWithChildrenAsync_PreservesParentTemplateId_ForInheritanceChainWalk()
     {