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, 50 insertions, 0 deletions

diff --git a/libs/preview_nif/data/shaders/default.vert b/libs/preview_nif/data/shaders/default.vert
new file mode 100644
index 0000000..90cccd3
--- /dev/null
+++ b/libs/preview_nif/data/shaders/default.vert
@@ -0,0 +1,50 @@
+#version 120
+
+uniform mat4 modelViewMatrix;
+uniform mat4 mvpMatrix;
+uniform mat3 normalMatrix;
+uniform vec3 lightDirection;
+uniform vec4 ambientColor;
+uniform vec4 diffuseColor;
+
+attribute vec3 position;
+attribute vec3 normal;
+attribute vec3 tangent;
+attribute vec3 bitangent;
+attribute vec2 texCoord;
+attribute vec4 color;
+
+varying vec2 TexCoord;
+varying vec3 LightDir;
+varying vec3 ViewDir;
+
+varying vec3 N;
+varying vec3 t;
+varying vec3 b;
+varying vec3 v;
+
+varying vec4 A;
+varying vec4 C;
+varying vec4 D;
+
+void main( void )
+{
+    gl_Position = mvpMatrix * vec4(position, 1.0);
+    TexCoord = texCoord;
+
+    N = normalize(normalMatrix * normal);
+    t = normalize(normalMatrix * tangent);
+    b = normalize(normalMatrix * bitangent);
+    v = vec3(modelViewMatrix * vec4(position, 1.0));
+
+    mat3 tbnMatrix = mat3(b.x, t.x, N.x,
+                          b.y, t.y, N.y,
+                          b.z, t.z, N.z);
+
+    ViewDir = tbnMatrix * -v;
+    LightDir = tbnMatrix * lightDirection;
+
+    A = ambientColor;
+    C = color;
+    D = diffuseColor;
+}