Frame Home on a PC with SteamVR (Windows, Linux); thumbnails from the spawn

- src/home_platform.h: what Frame Home and the panel need from the system (paths, finding and stopping each
  other, running a tool, restarting, priorities) for SteamOS, Windows and Linux PCs. On a PC the environments are
  Frame Studio's My Environments; Frame Home's own files in %LOCALAPPDATA%\Frame Home (Windows).
- src/openvr_loader.cpp: a PC build finds SteamVR's own OpenVR library at run time (openvrpaths.vrpath), so it runs
  on any PC with SteamVR; Vulkan through volk. CMake: FRAME_HOME_PC (default on Windows and x86-64 Linux); the Steam
  Frame build is unchanged.
- Windows: Frame Home is SteamVR's home app; SteamVR's classic environment shows a 360-degree picture of the current
  home from its spawn (frame-home --panorama --spawn, made by the panel when the home changes) instead of Aurora
  while Frame Home starts. Linux PCs: the Steam Frame's compositor layer, as on the headset.
- frame/pc: install-frame-home-pc.ps1 (+ .bat): online through SteamVR's API or offline in its config files; the
  SteamVR settings it changes are saved and restored exactly on -Uninstall (tested in a sandbox both ways).
  frame-switcher --uninstall. Studio: Properties > Headset > This PC installs it from pc/ beside Studio.
- Packaging and CI: pc/ in the Windows x64 and Linux x64 Studio downloads; FrameHome-PC-windows-x64.zip.
- Thumbnails come from where Frame Home starts you (the first spawn, eyes 1.6 m up): Studio's saves and the
  panel's (frame-home --snapshot --spawn).
- docs/pc-steamvr.md.

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

docs/README.md

@@ -10,5 +10,6 @@
 | [Performance](performance.md) | How Frame Home reaches 120 fps, checking it, fixing stutter, Studio's own pacing |
 | [Frame Studio guide](studio-guide.md) | The Studio window, tools and panels |
 | [Bundles](bundles.md) | Several environments in one `.fbundle` file |
+| [Frame Home on a PC](pc-steamvr.md) | Your homes as SteamVR's environment on a Windows or Linux PC |
 | [Building from source](building.md) | Building on each system, the CI, the headset side, the repository layout |
 | [Troubleshooting](troubleshooting.md) | Symptoms and fixes, logs, the self-test |

docs/pc-steamvr.md

@@ -0,0 +1,58 @@
+# Frame Home on a PC (SteamVR)
+
+Frame Home also runs on a PC with SteamVR: the same renderer, homes and settings as on the Steam Frame, as SteamVR's
+environment whenever no game is open. The **Environments** panel in the Steam menu switches homes, as on the headset.
+It works with any headset SteamVR drives, including a Steam Frame streaming from the PC.
+
+On a PC, Frame Home shows the environments in Frame Studio's **My Environments** (`Documents\Frame Studio\Environments`):
+save something in Studio and it's in VR straight away. Bundles (`.fbundle`) dropped there are unpacked by the panel.
+
+## Install
+
+**From Frame Studio:** **Properties > Headset**, section **This PC**: **Install Frame Home on This PC**. The same button
+updates it after you update Studio; **Remove from This PC** takes it off.
+
+**Without Studio (Windows):** download `FrameHome-PC-windows-x64.zip` from the
+[latest build](https://github.com/Toastconcern/FrameStudio/releases), unzip it, and double-click
+**Install Frame Home on this PC.bat** (or **Remove Frame Home from this PC.bat**). From a terminal:
+
+```powershell
+powershell -ExecutionPolicy Bypass -File install-frame-home-pc.ps1              # install or update
+powershell -ExecutionPolicy Bypass -File install-frame-home-pc.ps1 -Uninstall   # SteamVR's own environment back
+```
+
+SteamVR can be running or not: running, the change happens at once; not running, it's written to SteamVR's settings
+and takes effect when SteamVR starts.
+
+## How it works
+
+**Windows.** Frame Home becomes SteamVR's *home app*: SteamVR starts it whenever no game is open, and brings it back
+when a game quits. For the moments before it draws (SteamVR starting, a game closing) SteamVR shows its classic
+environment instead of Aurora, with its background set to a 360-degree picture of your current home taken from its
+spawn. So you see your home, not Aurora. The panel makes a new picture whenever you switch homes.
+
+**Linux.** Exactly the Steam Frame's way: a small Vulkan layer in SteamVR's compositor draws Frame Home in Aurora's
+place, and `frame-home --system` renders it. (Linux PCs are supported but haven't been tested on a desktop yet.)
+
+The installer saves the SteamVR settings it changes (`enableHomeApp`, `environmentMode`, `background` and its
+projection) and puts them back exactly when you remove Frame Home.
+
+## Files
+
+| Where | What |
+|---|---|
+| `%LOCALAPPDATA%\Frame Home\bin` | `frame-home.exe`, `frame-switcher.exe` |
+| `%LOCALAPPDATA%\Frame Home\current` | the environment shown |
+| `%LOCALAPPDATA%\Frame Home\settings.json` | Frame Home's settings (the panel's Settings page) |
+| `%LOCALAPPDATA%\Frame Home\logs` | logs |
+| `%LOCALAPPDATA%\Frame Home\background` | the picture SteamVR shows while Frame Home starts |
+| `Documents\Frame Studio\Environments` | the environments |
+
+On Linux everything is in `~/frame-home`, as on the headset.
+
+## Troubleshooting
+
+- **Aurora still shows after installing:** SteamVR was running with its settings window open; restart SteamVR.
+- **Nothing in the Steam menu:** the panel starts with SteamVR. In SteamVR's settings, **Startup / Shutdown > Choose
+  Startup Overlay Apps** should list **Environments** switched on.
+- **Black world:** Frame Home needs a GPU with Vulkan 1.2. Its log is `%LOCALAPPDATA%\Frame Home\logs\frame-home.log`.

docs/studio-guide.md

@@ -160,6 +160,8 @@ The **Headset** tab (or the **Headset** menu):
 - **Send to Frame** makes the open environment the headset's current one, saved or not.
 - **Install Frame Home** puts Frame Home itself on the headset, with the environments and bundles you list under
   **Environments to install**. **Restore SteamVR's Environment** takes it off again.
+- **This PC** (Windows and Linux): **Install Frame Home on This PC** makes your environments SteamVR's environment on
+  the computer Studio runs on. See [pc-steamvr.md](pc-steamvr.md).
 - The **Headset** field is the headset's address: an SSH alias such as `frame`, or `steamos@<address>`.
   See [headset-setup.md](headset-setup.md) and [install-frame-home.md](install-frame-home.md).