fix #425: pack resident budget is a 1080p ceiling that scales with pixel count; an explicit Apply retries a failed selection

Live Holtburg at 2560x1440: the Low preset needed 67,368,164 resident bytes
(screen-sized HDR/depth/ray targets are 44 MB of that) against an absolute
64 MiB ceiling that had only been validated at 1080p, so Options -> Apply
fell back to the default path; every later Apply was then refused by the
controller's failure memo, which treated the user's deliberate choice like
automatic re-activation.

RenderPackResidentBudget.Effective scales the declared 1080p figure by the
viewport's pixel-count ratio (never below 1), still capped by the hardware
MaxPackResidentBytes; both pack graphs use it and the performance-matrix
tool judges its resident column by the same rule (contract test updated).
RenderPackController.Request gains explicitUserChoice, which clears the
memo for that selection; RenderPackSelectionBinding passes it on every
display edge (Apply, including resolution changes) and keeps the memo for
the startup request.

Tests: RenderPackResidentBudgetTests (1080p/720p keep the declared
ceiling, 1440p = 16/9x, 4K = 4x, hardware cap wins, zero extent rejected);
controller explicit-retry; the binding test now proves the user's next
Apply activates once the cause is gone. App hermetic lane 6,068/0 (Release).

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

src/AcDream.App/Rendering/Packs/DeclaredFullscreenRenderPackGraph.cs

@@ -268,8 +268,10 @@ internal class DeclaredFullscreenRenderPackGraph :
         TargetSet? prior = _targets;
         _targets = candidate;
         _resourceBudget = budget;
-        _residentGpuBudgetBytes = Math.Min(
+        _residentGpuBudgetBytes = RenderPackResidentBudget.Effective(
             Preset.MaxResidentGpuBytes,
+            width,
+            height,
             capabilities.MaxPackResidentBytes);
         _resourceGeneration = checked(_resourceGeneration + 1);
         _renderedFrame = false;