Build: require 64-bit Windows — PlatformTarget x64 in app + tests (bundled ffmpeg is win64, ONNX Runtime has no win-x86, 32-bit address space can't hold 1080p buffers) (Unit: 64-bit requirement)

ai.md

@@ -2245,6 +2245,13 @@ before re-deriving it. Executable checklist: `TASKS/task-48-distribution-msix.md
   thinks I'm expired" bug class along with the offline-grace machine.
 - **⛔ Bundle ffmpeg — no runtime downloads** (Store policy 10.2.2; also the 2026-09-01 404).
   See the FFmpeg locator section above. **This is the first code unit.**
+- **⛔ 64-bit Windows only (creator ruling 2026-10-09).** Both csproj files set
+  `<PlatformTarget>x64</PlatformTarget>` (the test project too — an AnyCPU test project
+  referencing an x64 app raises MSB3270 and breaks the 0-warning gate). Why: the bundled ffmpeg
+  is the win64 build, ONNX Runtime 1.31 ships no win-x86 native (only win-x64/win-arm64), and a
+  32-bit address space can't hold the 1080p frame buffers. Windows 11 is 64-bit-only anyway. The
+  MSIX publish targets x64 only (ARM64 is a possible later add: both ffmpeg and ONNX Runtime have
+  arm64 builds). Public copy says "64-bit Windows 10 or 11".
 
 **What does NOT change: the monetization posture.** Free gets everything; the branding flash
 stays the **only** paid delta (`TASK 36` item 2). Store IAP changes how `IsPremium` is