chore: low-severity sweep — import session cap, full compile-error lists, leaf-name-fallback validation warning

#05-T24. Three low-severity cleanups, each TDD'd:
- TransportOptions.MaxConcurrentImportSessions (8): BundleSessionStore.Open rejects
  a new session past the cap (evicting expired entries first), bounding the N×~200 MB
  decrypted-content footprint. Soft cap (count/add not atomic).
- ScriptCompiler.TryCompile now joins ALL forbidden-API violations / compile errors
  (string.Join instead of [0]) so an operator sees every problem at once; the T15
  verdict cache stores the joined string.
- SemanticValidator emits an advisory warning when a CallScript target resolves
  ONLY via the composed leaf-name fallback (dynamic child path, not statically
  verified) instead of silently accepting it.

Claude-Session: https://claude.ai/code/session_01MtdgwpEeCUn6cUA5f1LMPj

tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Validation/ScriptCompilerTests.cs

@@ -40,6 +40,19 @@ public class ScriptCompilerTests
         Assert.Contains("forbidden", result.Error, StringComparison.OrdinalIgnoreCase);
     }
 
+    [Fact]
+    public void TryCompile_MultipleForbiddenApis_ReportsAll()
+    {
+        // #05-T24: the failure message must enumerate EVERY forbidden API, not
+        // just the first, so an operator fixing one isn't surprised by the next.
+        var result = _sut.TryCompile(
+            "System.IO.File.ReadAllText(\"x\"); System.Diagnostics.Process.Start(\"y\");",
+            "Test");
+        Assert.True(result.IsFailure);
+        Assert.Contains("System.IO", result.Error, StringComparison.Ordinal);
+        Assert.Contains("Process", result.Error, StringComparison.Ordinal);
+    }
+
     [Theory]
     // Namespace alias — the old substring scan never saw "System.IO." spelled out.
     [InlineData("using IO = System.IO; IO.File.ReadAllText(\"x\");")]