Fix the Linux build of the qt6 branch, compile QML to bytecode only

- Remove Core5Compat (unused, not part of the Steam Frame's system Qt).
- Request GuiPrivate explicitly (required since Qt 6.10 for QRhi); temporary
  until rendering moves to public API.
- Compile QML to bytecode only: C++ generated from QML uses private Qt API
  that only matches the exact Qt version it was built with.
- Pick the OpenVR library per architecture (linux64, linuxarm64, win64) for
  linking and for the copy next to the binary; RPATH $ORIGIN.
- Link libXtst, needed by input_sender_X11.cpp.
- Include d3d11.h and handle QRhi::D3D11 only on Windows.
- Replace leftover easylogging LOG(INFO) calls with qInfo().

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/steamframe/PROGRESS.md

@@ -0,0 +1,28 @@
+# Steam Frame port: progress
+
+## Iteration 1
+
+### Step 1: build fixes, bytecode-only QML (2026-10-07)
+
+**Changes:**
+- **`CMakeLists.txt`:**
+  - `Core5Compat` removed (unused, not on the Frame).
+  - `GuiPrivate` requested explicitly. This is temporary, until step 3 replaces QRhi.
+  - `QT_QMLCACHEGEN_ARGUMENTS --only-bytecode`.
+  - OpenVR library directory per architecture (`linux64` / `linuxarm64` / `win64`), for
+    linking and for the copy next to the binary.
+  - `RPATH $ORIGIN`.
+  - `libXtst` linked.
+- **`overlaycontroller.cpp`:** `d3d11.h` and `case QRhi::D3D11` only under `_WIN32`.
+- **Logging:** 8 active easylogging `LOG(INFO)` calls became `qInfo()`
+  (`overlaycontroller.cpp` 6, `ChaperoneTabController.cpp` 1,
+  `MoveCenterTabController.cpp` 1). Commented-out `LOG` lines are left unchanged.
+- Only changed lines are formatted (`git clang-format`).
+
+**Results (x86_64, Arch, Qt 6.11.1, GCC):**
+- The build succeeds, with 1463 compiler warnings, as in `qt6`.
+- `objdump -T`: 7 `Qt_6_PRIVATE_API` symbols, all `QRhi…` (step 3). The
+  `QQmlPrivate::AOTCompiledContext` symbols are gone (bytecode-only QML).
+- `libopenvr_api.so` is resolved from the binary's directory (`ldd`).
+- Not started: without a running SteamVR the start hangs in OpenVR init (expected; tested
+  on the Frame in step 5).