Fix OptiScaler NGX routing and align marker polling defaults

- Explicitly route OptiScaler to d4r\nvngx.dll in release packages.

- Extract INI generation into a helper that preserves line endings
  and rejects missing or duplicate settings.

- Check NGX routing separately from file presence and return failure
  when the installation is incomplete or misconfigured.

- Add an optional OptiScaler patch for external DLSS backends while
  preserving AMD identity for FSR4, with matching launch guidance.

- Align portable and launcher marker polling defaults at 200 us.

- Log when d4r's model override replaces game or OptiScaler presets.

- Add configuration, package, routing and coexistence regression tests.

- Update installation documentation, add FSR/DLSS comparison videos
  and ignore local .tools artifacts.

Refs: #7, #14

docs/architecture.md

@@ -63,7 +63,7 @@ The release zip (`scripts/package_release.sh`) is unpacked into the folder that
 
 | File | Role |
 |---|---|
-| `dxgi.dll`, `OptiScaler.ini` | OptiScaler 0.9.4. Its INI sets DLSS as the DX12 upscaler and `OptiDllPath=d4r`, so OptiScaler loads the shim as `d4r\nvngx.dll`. |
+| `dxgi.dll`, `OptiScaler.ini` | OptiScaler 0.9.4. Its INI sets DLSS as the DX12 upscaler, `NvngxPath=d4r\nvngx.dll` to select the shim explicitly, and `OptiDllPath=d4r` for the other libraries. |
 | `d3d12.dll`, `d3d12core.dll` | the d4r-patched vkd3d-proton. Proton loads DLLs from the game folder before `system32`. |
 | `d4r\nvngx.dll`, `d4r\nvcuda.dll` | the shim and the CUDA bridge |
 | `d4r\zluda\libcuda.so` | ZLUDA |
@@ -71,6 +71,12 @@ The release zip (`scripts/package_release.sh`) is unpacked into the folder that
 | `d4r\d4r.ini` | this game's settings |
 | `d4r\nvngx_dlss.dll`, `d4r\ngx\_nvngx.dll` | NVIDIA's files (the packager's `D4R_BUNDLE_NVIDIA=0` leaves them for the user to add) |
 
+**NGX routing.** OptiScaler tries `_nvngx.dll` before `nvngx.dll`, with system fallback for each name. `OptiDllPath=d4r` alone can therefore select Proton's system `_nvngx.dll` before reaching the shim. A file-valued `NvngxPath` takes priority on the first probe, regardless of the probe's name. It must select `d4r\nvngx.dll`, never `d4r\ngx\_nvngx.dll`: the latter is NVIDIA's core, which the shim loads internally. See OptiScaler 0.9.4's [NGX loader](https://github.com/optiscaler/OptiScaler/blob/v0.9.4/OptiScaler/proxies/NVNGX_Proxy.h) and [override handling](https://github.com/optiscaler/OptiScaler/blob/v0.9.4/OptiScaler/Util.cpp).
+
+OptiScaler 0.9.4 checks a relative `NvngxPath` against the process working directory; it does not anchor that override to the executable like it does `OptiDllPath`. The portable INI assumes the game's working directory is the executable folder. Launchers that use another working directory need an absolute Windows filename for the shim. The Proton developer game launcher and OptiScaler harness already generate that form for `bin/d4r_nvngx.dll`.
+
+`sh d4r/d4r-check.sh` checks file presence and the explicit NGX route separately; it does not prove runtime initialization. OptiScaler's startup `nvngx.dll not found!` warning checks the executable folder and already loaded modules, not the override. It can appear before the shim loads from `d4r/`; verify the later `NVNGXProxy::InitNVNGX Loaded from ...\d4r\nvngx.dll` line and `d4r/d4r_nvngx.log` instead. Keep the shim in `d4r/`.
+
 **Settings.** When an `d4r.ini` sits next to the shim, the shim turns it into the same environment variables the developer launcher sets, with the release's defaults. A variable that is already set, for example in the launch options, wins. Settings for the Linux side (ZLUDA's and the bridge's) are handed to the bridge through `d4rSetEnv` right after it is loaded, before its first CUDA call.
 
 **Loading ROCm.** Steam runs GE-Proton 11 inside its container runtime (SteamLinuxRuntime_4), whose library search path has no ROCm. The bridge therefore: