Add Steam Linux Runtime (SLR) support + fix Use Proton default

Steam Linux Runtime:
- New Rust module (libs/nak/src/slr.rs): download SteamLinuxRuntime_sniper
  from repo.steampowered.com, SHA256 verification, BUILD_ID update checks
- nak_ffi exports: nak_slr_is_installed, nak_slr_get_run_script, nak_download_slr
- ProtonLauncher: wraps Proton launch inside SLR pressure-vessel container
  when enabled (run -- proton waitforexitandrun game.exe)
- Instance Manager: SLR checkbox (default on) beside Steam DRM checkbox
- Main window: pre-check downloads SLR before launch if needed
- Proton settings tab: "Download Steam Linux Runtime" button
- spawn.cpp: reads fluorine/use_slr per-instance INI key
- Logs "Final command:" showing full assembled launch command

Bug fixes:
- Fix Use Proton off by default for plugin executables (executableslist.cpp)
- Fix Use Proton off by default for file tree right-click (filetree.cpp)
- Fix Fedora 43 Qt platform plugin crash: explicit QT_QPA_PLATFORM_PLUGIN_PATH
- Add Qt6::Concurrent to CMakeLists for QtConcurrent background downloads

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

1 files changed, 25 insertions, 1 deletions

diff --git a/libs/nak_ffi/include/nak_ffi.h b/libs/nak_ffi/include/nak_ffi.h
index e1a9185..7a40863 100644
--- a/libs/nak_ffi/include/nak_ffi.h
+++ b/libs/nak_ffi/include/nak_ffi.h
@@ -176,7 +176,31 @@ char *nak_ensure_dxvk_conf(void);
 char *nak_get_dxvk_conf_path(void);

 

 /* ========================================================================

- * Tier 8: PE Icon Extraction

+ * Tier 8: Steam Linux Runtime (SLR)

+ * ======================================================================== */

+

+/** Returns 1 if SteamLinuxRuntime_sniper is installed and the run script exists, 0 otherwise. */

+int nak_slr_is_installed(void);

+

+/** Get the path to the SLR run script.

+ *  Returns NULL if SLR is not installed.

+ *  Caller must free with nak_string_free(). */

+char *nak_slr_get_run_script(void);

+

+/** Download and install SteamLinuxRuntime_sniper from Valve's repo (~180 MB).

+ *  Skips if already at the latest version (checked via BUILD_ID).

+ *  progress_cb: 0.0..1.0 during download (may be NULL).

+ *  status_cb: human-readable status strings (may be NULL).

+ *  cancel_flag: pointer to int, set non-zero to cancel (may be NULL).

+ *  Returns NULL on success, or error message (free with nak_string_free). */

+char *nak_download_slr(

+    NakProgressCallback progress_cb,

+    NakStatusCallback status_cb,

+    const int *cancel_flag

+);

+

+/* ========================================================================

+ * Tier 9: PE Icon Extraction

  * ======================================================================== */

 

 /** Result of icon extraction */