Remove the pc-streaming folder

Deletes pc-streaming/ (the experimental Windows D3D11 compositor proxy that
tried to make a home SteamVR's environment on a tethered PC, with its .def,
installer .ps1/.bat and notes) and everything that pointed at its files:

- CMakeLists: the frame-home-d3d11 proxy target.
- build-studio.sh: the Windows pc/ staging and the d3d11.dll build step.
- CI: the pc-home-windows job and the Windows Studio job's download/staging
  of FrameHome-PC-windows-x64.
- Studio: the Windows branch of the "This PC" installer (it ran the deleted
  .ps1); the feature is now Linux-only, where it installs the Vulkan layer.
- README and docs: the Windows PC download row, the PC-streaming highlight,
  and the dead Frame-Home-on-a-PC / pc-steamvr.md links.

FRAME_HOME_PC and the runtime OpenVR/Vulkan loader stay, so Frame Home still
builds for a PC; only the pc-streaming folder and its wiring are gone. The
Linux PC layer (layer/) and its install path are untouched.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

studio/studio.cpp

@@ -5354,17 +5354,15 @@ struct Studio {
     }
 
     // ── This PC: Frame Home as SteamVR's environment on the computer Studio runs on (the installer beside Studio,
-    // pc/: install-frame-home-pc.ps1 on Windows, install.sh on Linux). It shows My Environments, so what's saved here
-    // is in VR straight away; the Environments panel in the Steam menu switches them.
+    // pc/install.sh, Linux only). It shows My Environments, so what's saved here is in VR straight away; the
+    // Environments panel in the Steam menu switches them.
     std::thread pcJob;
     std::atomic<bool> pcBusy{false};
     std::string pcStatus;                    // (statusMutex)
     fs::path pcPayload() const { return exeDir() / L"pc"; }
     bool pcAvailable() const {
-#if defined(_WIN32)
-        return fs::exists(pcPayload() / L"install-frame-home-pc.ps1");
-#elif defined(__APPLE__)
-        return false;                        // (no SteamVR for macOS)
+#if defined(_WIN32) || defined(__APPLE__)
+        return false;                        // (Linux only: no SteamVR on macOS; no PC compositor layer on Windows)
 #else
         return fs::exists(pcPayload() / L"install.sh");
 #endif
@@ -5385,12 +5383,7 @@ struct Studio {
         pcBusy = true;
         { std::lock_guard<std::mutex> l(statusMutex); pcStatus = uninstall ? "Giving SteamVR its own environment back\u2026" : "Installing\u2026"; }
         pcJob = std::thread([this, uninstall] {
-#ifdef _WIN32
-            const std::string cmd = "powershell -NoProfile -ExecutionPolicy Bypass -File \"" + narrow((pcPayload() / L"install-frame-home-pc.ps1").wstring()) + "\"" +
-                                    (uninstall ? " -Uninstall" : "");
-#else
             const std::string cmd = "sh \"" + narrow((pcPayload() / L"install.sh").wstring()) + "\"" + (uninstall ? " uninstall" : "");
-#endif
             std::string out;
             const int rc = platform::run(cmd, pcPayload(), out);
             std::string msg = lastLine(out);   // the installer's verdict: its last "frame-install:" line