feat(pipeline): MP0 - wire FrameProfiler into GameWindow + DebugPanel toggle

GameWindow gets one field (_frameProfiler), one FrameBoundary() call at
the top of OnRender, three stage scopes (Update in OnUpdate, Upload
around _wbMeshAdapter?.Tick(), ImGui around _imguiBootstrap.Render()),
and one Dispose() call in teardown before _dats?.Dispose() releases the
GpuFrameTimer query ring. No new feature bodies land in GameWindow.cs —
all profiler logic lives in AcDream.App.Diagnostics.

DebugVM.FrameProf mirrors RenderingDiagnostics.FrameProfEnabled so the
DebugPanel checkbox ("Frame profiler ([frame-prof])") toggles the 5s
report live. Note: the checkbox lives in
AcDream.UI.Abstractions/Panels/Debug/DebugPanel.cs (IPanelRenderer,
backend-agnostic) alongside the other Diagnostics-section checkboxes —
not in AcDream.UI.ImGui, which holds no panel-drawing code per Code
Structure Rule 3.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/AcDream.UI.Abstractions/Panels/Debug/DebugPanel.cs

@@ -254,6 +254,12 @@ public sealed class DebugPanel : IPanel
         if (r.Checkbox("Probe auto-walk (ACDREAM_PROBE_AUTOWALK)",
                        ref probeAutoWalk))                              _vm.ProbeAutoWalk = probeAutoWalk;
 
+        // MP0 (2026-07-05): permanent frame profiler toggle — not a
+        // throwaway investigation probe, so it lives with the other
+        // always-available diagnostics rather than a dated section.
+        bool frameProf = _vm.FrameProf;
+        if (r.Checkbox("Frame profiler ([frame-prof])", ref frameProf)) _vm.FrameProf = frameProf;
+
         // ── Indoor rendering diagnostics (2026-05-19) ───────────────
         // Pinpoint where the EnvCell rendering chain breaks for
         // hypothesis-driven Phase 2 fix. Spec: