feat(ui/scripts): editor support for self/child/parent accessors

Phases 3+4 of the script-scope rollout. Wires the runtime accessors
landed in efba01d through to Monaco completion, diagnostics, and
hover.

New analyzer surface in ScriptAnalysisService:

  String-literal completion contexts (added to TryStringLiteralCompletions):
    Attributes["..."]                       -> SelfAttributes
    Children["..."]                         -> composition names
    Children["X"].Attributes["..."]         -> child template's attributes
    Children["X"].CallScript("...")         -> child template's scripts
    Parent.Attributes["..."]                -> parent template's attributes
    Parent.CallScript("...")                -> parent template's scripts

  Diagnostics:
    SCADA006   Attribute "Typo" is not declared on {this template,
               child composition 'X', the parent}.  (warning)
    SCADA007   Composition "Unknown" is not declared on this template.
               (warning)

  CallShared / CallScript snippet-expansion now routes through the
  child / parent shape catalogs when invoked on Children["X"] /
  Parent — picking a child script accepts `Sample", ${1:count})`.

Contract additions:
  - AttributeShape (Name, Type) record
  - CompositionContext (Name, Attributes, Scripts) record
  - SelfAttributes / Children / Parent fields on DiagnoseRequest,
    CompletionsRequest, HoverRequest, SignatureHelpRequest

ScriptHost (analyzer-side globals) gains stub AttributeBag /
ChildrenBag / CompositionBag types so Roslyn doesn't emit CS0103 on
Attributes / Children / Parent. The stubs are never invoked — only
their signatures are read by the analyzer's compilation pass.

MonacoEditor.razor exposes SelfAttributes / Children / Parent
parameters; GetContext returns them; monaco-init.js forwards all
three on completion / hover / signature-help / diagnostics requests.

TemplateEdit fetches each composition's resolved child template
shape via GetTemplateWithChildrenAsync, and queries GetAllTemplatesAsync
for any single parent that composes the open template. Multi-parent
or no-parent → Parent is suppressed.

11 new xUnit tests on the new completion / diagnostic paths. Total:
149 -> 159.

Browser-verified via curl:
  - Children["..."] suggests composition names
  - Attributes["..."] suggests attributes with type detail
  - Attributes["Typo"] squiggles SCADA006
  - Children["Unknown"] squiggles SCADA007
  - No spurious CS0103 on the new accessors

Hover, signature help, and inlay hints for the new accessors keep
working because they reuse the same dispatch logic.

src/ScadaLink.CentralUI/Components/Shared/MonacoEditor.razor

@@ -48,6 +48,26 @@
     /// </summary>
     [Parameter] public IReadOnlyList<ScriptAnalysis.ScriptShape>? SiblingScripts { get; set; }
 
+    /// <summary>
+    /// Attributes declared on the current template. Surfaced inside
+    /// <c>Attributes["..."]</c> for completion and SCADA006 diagnostics.
+    /// </summary>
+    [Parameter] public IReadOnlyList<ScriptAnalysis.AttributeShape>? SelfAttributes { get; set; }
+
+    /// <summary>
+    /// Child compositions on the current template, each with its template's
+    /// attributes and scripts. Surfaced for <c>Children["X"].Attributes</c>,
+    /// <c>Children["X"].CallScript</c>, and SCADA007 diagnostics.
+    /// </summary>
+    [Parameter] public IReadOnlyList<ScriptAnalysis.CompositionContext>? Children { get; set; }
+
+    /// <summary>
+    /// Parent template when the current template is composed inside exactly
+    /// one other template. <c>null</c> at the root or when multiple parents
+    /// exist. Surfaced for <c>Parent.Attributes</c> / <c>Parent.CallScript</c>.
+    /// </summary>
+    [Parameter] public ScriptAnalysis.CompositionContext? Parent { get; set; }
+
     /// <summary>
     /// Fires whenever Monaco's marker set updates (after the 500 ms diagnostic
     /// debounce). Hosts can render a <see cref="ProblemsPanel"/> with the same
@@ -125,7 +145,10 @@
         SiblingScripts?.ToArray() ?? Array.Empty<ScriptAnalysis.ScriptShape>(),
         DeclaredParameterShapes?.ToArray()
             ?? DeclaredParameters?.Select(n => new ScriptAnalysis.ParameterShape(n, "Object", true)).ToArray()
-            ?? Array.Empty<ScriptAnalysis.ParameterShape>());
+            ?? Array.Empty<ScriptAnalysis.ParameterShape>(),
+        SelfAttributes?.ToArray() ?? Array.Empty<ScriptAnalysis.AttributeShape>(),
+        Children?.ToArray() ?? Array.Empty<ScriptAnalysis.CompositionContext>(),
+        Parent);
 
     private async Task FormatAsync()
     {
@@ -163,5 +186,8 @@
     public record ScadaContext(
         string[] DeclaredParameters,
         ScriptAnalysis.ScriptShape[] SiblingScripts,
-        ScriptAnalysis.ParameterShape[] DeclaredParameterShapes);
+        ScriptAnalysis.ParameterShape[] DeclaredParameterShapes,
+        ScriptAnalysis.AttributeShape[] SelfAttributes,
+        ScriptAnalysis.CompositionContext[] Children,
+        ScriptAnalysis.CompositionContext? Parent);
 }