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, 33 insertions, 0 deletions

diff --git a/libs/preview_nif/src/preview_nif_en.ts b/libs/preview_nif/src/preview_nif_en.ts
new file mode 100644
index 0000000..10b8b07
--- /dev/null
+++ b/libs/preview_nif/src/preview_nif_en.ts
@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE TS>
+<TS version="2.1" language="en_US">
+<context>
+    <name>NifWidget</name>
+    <message>
+        <location filename="NifWidget.cpp" line="92"/>
+        <source>OpenGL debug message: %1</source>
+        <translation type="unfinished"></translation>
+    </message>
+</context>
+<context>
+    <name>PreviewNif</name>
+    <message>
+        <location filename="PreviewNif.cpp" line="57"/>
+        <source>Failed to load file: %1</source>
+        <translation type="unfinished"></translation>
+    </message>
+    <message>
+        <location filename="PreviewNif.cpp" line="87"/>
+        <source>Verts: %1 | Faces: %2 | Shapes: %3</source>
+        <translation type="unfinished"></translation>
+    </message>
+</context>
+<context>
+    <name>QObject</name>
+    <message>
+        <location filename="TextureManager.cpp" line="118"/>
+        <source>Failed to interface with managed game plugin</source>
+        <translation type="unfinished"></translation>
+    </message>
+</context>
+</TS>