Add NIF previewer plugin with Linux-specific fixes

Vendored from github.com/Parapets/mo2-preview_nif and adapted for Linux:

- BSA texture resolution via MO2 virtual tree with case-insensitive
  fallback walk (Linux FS is case-sensitive; NIFs reference textures
  with arbitrary case against files on disk)
- Process-wide cached BSA candidate list, keyed by profile path,
  priority-sorted, filtering disabled mods
- Path backslash normalization before loose-file lookup
- Polygon offset on SLSF1_Decal-flagged shapes to break z-ties with
  coincident base meshes (road decals, moss overlays)
- Opaque framebuffer via glColorMask alpha lock so alpha-blended shapes
  can't bleed the dialog background through the preview area
- QMouseEvent::globalPosition().toPoint() for Qt6 compatibility

Preview dialog behavior (organizercore.cpp):
- Switch previewFile and previewFileWithAlternatives from stack-allocated
  exec() to heap + ApplicationModal + show() + WA_DeleteOnClose.
- Parent passed as nullptr so preview lifetime is decoupled from the
  stack-allocated ModInfoDialog that spawns it. Nested exec() inside
  the enclosing dialog's exec() was softlocking on close.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

1 files changed, 34 insertions, 0 deletions

diff --git a/libs/preview_nif/CMakeLists.txt b/libs/preview_nif/CMakeLists.txt
new file mode 100644
index 0000000..7db3db2
--- /dev/null
+++ b/libs/preview_nif/CMakeLists.txt
@@ -0,0 +1,34 @@
+cmake_minimum_required(VERSION 3.22)
+
+project(preview_nif CXX)
+
+include(FetchContent)
+
+# gli (texture loader — header-only, needs glm)
+FetchContent_Declare(
+    gli
+    GIT_REPOSITORY https://github.com/g-truc/gli.git
+    GIT_TAG        master
+)
+set(GLI_TEST_ENABLE OFF CACHE BOOL "Build gli unit tests")
+
+# nifly (NIF parser)
+FetchContent_Declare(
+    nifly
+    GIT_REPOSITORY https://github.com/ousnius/nifly.git
+    GIT_TAG        main
+)
+
+FetchContent_MakeAvailable(gli nifly)
+
+# mo2_install_target compatibility shim (upstream uses mo2_install_target;
+# Fluorine defines mo2_install_plugin).
+if(NOT COMMAND mo2_install_target AND COMMAND mo2_install_plugin)
+    function(mo2_install_target target)
+        mo2_install_plugin(${target})
+    endfunction()
+endif()
+
+add_subdirectory(src)
+
+target_link_libraries(preview_nif PRIVATE nifly gli)