Add a Steam Frame flavour of the Android app with Frame controller bindings

The Steam Frame runs Android apps through Lepton with SteamVR's OpenXR
runtime. A third headset flavour, steamFrame, targets it:

- -mcpu=cortex-x4+nosve for the Snapdragon 8 Gen 3 (its firmware does
  not expose SVE, which clang otherwise auto-vectorises with), from one
  flavour-to-CPU map that the kit export now reads instead of guessing
  from the variant name.
- MKW_ANDROID_HEADSET=steam_frame defines MKW_HEADSET_STEAM_FRAME for
  the runtime's own targets, for Frame-specific defaults.
- A manifest without the Horizon OS entries, and FrameEntryActivity as
  the single real MAIN/LAUNCHER activity with the Khronos and Oculus VR
  categories, which Lepton needs to start an app in VR. It opens the
  setup panel and, when the selected game can start, the game on top.
- XR_VALVE_frame_controller_interaction: the Frame controller profile
  with its left D-pad (new dpad_* actions, the Wii Remote's D-pad or the
  gamepad's), View as menu and the left shoulder as the panel button.
  Also requested on Windows for SteamVR streaming to a Frame.
- Build-Quest.ps1, Build-QuestGame.ps1 and Run-Quest.ps1 take
  -Headset frame.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019HBRGKTE1GnN2ah8gcZKr3

runtime/CMakeLists.txt

@@ -37,6 +37,21 @@ option(MKW_BUILD_PRODUCTS "Build translated WiiCompiled product targets" ON)
 # aurora-main and its third-party tree stay unaffected.
 set(MKW_PROJECT_COMPILE_DEFINITIONS NOMINMAX)
 
+# The Android headset family the build is for (the Gradle flavour passes it). The
+# Steam Frame build runs under SteamVR's Android runtime rather than Horizon OS and
+# takes its own defaults (runtime_config.h) through MKW_HEADSET_STEAM_FRAME. The
+# definition reaches every target below, so the game kit's recorded compile flags
+# carry it too.
+if(MKW_PLATFORM_ANDROID)
+    set(MKW_ANDROID_HEADSET "quest" CACHE STRING "Android headset family: quest (Meta Quest, any flavour) or steam_frame")
+    set_property(CACHE MKW_ANDROID_HEADSET PROPERTY STRINGS quest steam_frame)
+    if(MKW_ANDROID_HEADSET STREQUAL "steam_frame")
+        list(APPEND MKW_PROJECT_COMPILE_DEFINITIONS MKW_HEADSET_STEAM_FRAME=1)
+    elseif(NOT MKW_ANDROID_HEADSET STREQUAL "quest")
+        message(FATAL_ERROR "MKW_ANDROID_HEADSET must be quest or steam_frame, not '${MKW_ANDROID_HEADSET}'")
+    endif()
+endif()
+
 set(CMAKE_CXX_STANDARD 17)
 
 # Declared before the vendored libraries so the third-party block below can