feat(code-editor): DebugValueHintsLayer + IDebugValueProvider — inline debug value overlay

[abbaye]

Context

New DrawingVisual overlay renders = <value> grey pills after identifiers during a debug pause (commit 56513b0a). Closes #84.

What changed

• DebugValueHintsLayer: DrawingVisual overlay, no-op until a provider is set
• IDebugValueProvider contract: set via SetDebugValueProvider()
• DebugValueHint DTO
• Reuses CE_InlayHintForeground / CE_InlayHintBackground theme tokens
• Same 500ms DispatcherTimer debounce as LspInlayHintsLayer
• Folder named Debugging/ (not Debug/) to avoid .gitignore [Dd]ebug/ rule

Files affected

• Layers/DebugValueHintsLayer.cs (new)
• Debugging/DebugValueHint.cs (new)
• Debugging/IDebugValueProvider.cs (new)
• Controls/CodeEditor.LSP.cs, CodeEditor.Rendering.cs, CodeEditor.cs

Follow-up

• Wire IDebugValueProvider from the Debugger module (Show line instead of position #44) when it lands
• Support multi-line / expandable value pills for collections