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, 36 insertions, 0 deletions

diff --git a/libs/preview_nif/src/CMakeLists.txt b/libs/preview_nif/src/CMakeLists.txt
new file mode 100644
index 0000000..28bb30f
--- /dev/null
+++ b/libs/preview_nif/src/CMakeLists.txt
@@ -0,0 +1,36 @@
+cmake_minimum_required(VERSION 3.22)
+
+find_package(Qt6 CONFIG REQUIRED COMPONENTS Widgets OpenGL OpenGLWidgets)
+find_package(fmt CONFIG REQUIRED)
+
+file(GLOB preview_nif_SOURCES CONFIGURE_DEPENDS
+    ${CMAKE_CURRENT_SOURCE_DIR}/*.cpp
+    ${CMAKE_CURRENT_SOURCE_DIR}/*.h
+)
+
+add_library(preview_nif SHARED ${preview_nif_SOURCES})
+
+mo2_configure_plugin(preview_nif NO_SOURCES WARNINGS OFF)
+
+target_include_directories(preview_nif PRIVATE
+    ${CMAKE_SOURCE_DIR}/libs/uibase/include/uibase/game_features
+    ${CMAKE_SOURCE_DIR}/libs/libbsarch/include/libbsarch
+)
+
+target_link_libraries(preview_nif PRIVATE
+    mo2::uibase
+    libbsarch
+    Qt6::Widgets
+    Qt6::OpenGL
+    Qt6::OpenGLWidgets
+    fmt::fmt
+)
+
+mo2_install_plugin(preview_nif)
+
+# Stage shader files next to the plugin under plugins/data/shaders/.
+install(
+    DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/../data/shaders
+    DESTINATION plugins/data
+    FILES_MATCHING PATTERN "*.vert" PATTERN "*.frag"
+)