fix(validation): close Theme 3 — 11 input-validation / unbounded-input findings

Each finding is a focused validation guard or upper bound at a trust boundary.
Highlights:
- Commons-015: EncryptionMetadata ctor now validates Algorithm (AES-256-GCM
  only), Kdf (PBKDF2-SHA256 only), Iterations ([100k, 10M]), non-null Salt/IV.
- Transport-004: new BundleUnlockRateLimiter (sliding-window, per-key,
  singleton) wired into BundleImporter.LoadAsync; over-budget callers see
  BundleUnlockRateLimitedException. Per-bundle 3-strike + per-window cap.
- ESG-022: ExternalSystemClient.InvokeHttpAsync allow-lists the documented
  GET/POST/PUT/PATCH/DELETE set (case-insensitive); unknown verbs throw.
- SEL-015: SiteEventLogger queue now bounded (10k cap, DropOldest); dropped
  events fault their Task and increment FailedWriteCount so the drop is
  observable instead of an unbounded memory growth.
- SEL-017: EventLogQueryService clamps caller-supplied PageSize to a new
  MaxQueryPageSize cap (default 500) so int.MaxValue can't OOM the host.
- SEL-020: LogEventAsync rejects severities outside {Info, Warning, Error}
  (matches SQLite BINARY-collation query filter).
- InboundAPI-020: ContentType "json" check now case-insensitive
  (application/JSON no longer slips through as not-json).
- InboundAPI-024: _knownBadMethods capped at 1000 entries (drops new entries
  once full); per-request DB lookup remains the correctness path.
- SR-025: HandleSetStaticAttribute validates the attribute name against the
  deployed config; unknown names now return Success=false instead of
  leaking orphan override rows into the SQLite store.
- TE-021: MoveTemplateAsync runs the sibling-name-collision check at the
  destination, mirroring TemplateFolderService.MoveFolderAsync.
- TE-022: LockEnforcer's once-locked-stays-locked rule now also covers
  LockedInDerived (was previously only IsLocked).

New regression tests across 8 test projects (EncryptionMetadata, rate
limiter, ESG client allow-list, SEL bounded channel / PageSize clamp /
severity validation, InboundAPI ContentType + bad-methods cap, SiteRT
unknown-attribute, TemplateEngine MoveTemplate + LockedInDerived).
Build clean; affected suites all green. README regenerated: 93 open (was 104).

Note: a separate manual re-run was needed for the SiteEventLogging hunk
because its initial subagent's source edits never landed on disk despite
reporting success (file-collision-style failure mode).

tests/ScadaLink.SiteRuntime.Tests/Actors/InstanceActorSetAttributeTests.cs

@@ -176,4 +176,41 @@ public class InstanceActorSetAttributeTests : TestKit, IDisposable
         Assert.Single(overrides);
         Assert.Equal("Backup", overrides["Label"]);
     }
+
+    // SiteRuntime-025: SetAttribute on an unknown attribute name must NOT
+    // pollute the in-memory dictionary, NOT publish a synthetic
+    // AttributeValueChanged, and NOT persist a durable override row.
+
+    [Fact]
+    public async Task SetAttribute_UnknownAttribute_ReturnsFailureAndDoesNotPersistOverride()
+    {
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "PumpUnknown",
+            Attributes =
+            [
+                new ResolvedAttribute { CanonicalName = "Label", Value = "Main", DataType = "String" }
+            ]
+        };
+        var dclProbe = CreateTestProbe();
+        var actor = CreateInstanceActor("PumpUnknown", config, dclProbe.Ref);
+
+        actor.Tell(new SetStaticAttributeCommand(
+            "corr-unknown", "PumpUnknown", "notARealAttr", "x", DateTimeOffset.UtcNow));
+
+        var response = ExpectMsg<SetStaticAttributeResponse>(TimeSpan.FromSeconds(5));
+        Assert.False(response.Success);
+        Assert.Contains("Unknown attribute", response.ErrorMessage);
+        Assert.Contains("notARealAttr", response.ErrorMessage);
+
+        // The DCL must NOT receive any write — the attribute does not exist.
+        dclProbe.ExpectNoMsg(TimeSpan.FromMilliseconds(300));
+
+        // No durable override row should be persisted for an unknown attribute —
+        // otherwise the polluting key resurrects on every restart via
+        // HandleOverridesLoaded.
+        await Task.Delay(300);
+        var overrides = await _storage.GetStaticOverridesAsync("PumpUnknown");
+        Assert.DoesNotContain("notARealAttr", overrides.Keys);
+    }
 }