Log SteamVR-started instances to logs/<exe>.log

The manifest passes --log-file, so a settings error (CFG-2) ends up in a
log file in the install folder. Package README and docs updated.

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

CLAUDE.md

@@ -240,6 +240,8 @@ hides world surfaces itself. Keep the teardown rule: overlays, then SteamVR, the
   RPATH `$ORIGIN/../lib`.
 - `manifest.vrmanifest` uses paths relative to itself, so `--install-manifest` works from both
   the build tree and an install.
+- The manifest passes `--log-file logs/<exe>.log` (`arguments`), so SteamVR-started instances
+  log to the install folder (or `build/<preset>/logs/` from the build tree).
 - `cmake/OpenVR.cmake` downloads only `openvr.h`, `LICENSE` and the matching
   `bin/linux64|linuxarm64/libopenvr_api.so` into `third_party/openvr-<ver>/` (gitignored).
 - **Deploying to the Frame uses its system Qt by default.** Bundling Qt is the fallback for