fix(dashboard): texture alpha in 3D scenery follows the game's shaders

The viewer treated every blended texture's alpha as opacity, so models
whose shader uses the alpha for something else rendered see-through. The
scenery manifest now carries each model's shader (RenderComponent.
shader_id via mapShaders) and the multishader tag table; meshes carry
their S##__ tag, read the way LWOBaseRenderComponent::AddObjectToRenderPipe
does (S%d, else _S%d, outside 3..108 the LEGO shader). Per res/shaders:
the LEGO lighting shaders lerp the texture over the vertex colors
(decal), LEGO items and terrain meshes ignore its alpha, everything else
keeps opacity. Pure rules unit tested.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/Dashboard.md

@@ -964,6 +964,10 @@ first; the detail setting picks the model level of detail, how far objects are d
 sharpness and a memory budget. Switch it off with *Scenery*. The 3D world view draws the same as its *Models* layer
 (on by default, Medium detail), plus the terrain's flairs. Converted models are cached in memory (64 MB) and in
 `dDashboardServer/scenery_cache` next to the server (at most 512 MB); nothing needs ImageMagick.
+Whether a texture's alpha makes a model see-through follows the shader the game draws it with (the render component's
+shader, or for a multishaded model the `S05__`-style tag in each part's name), not only the .nif: the LEGO shaders
+lay the texture over the vertex colors and terrain meshes and LEGO items ignore its alpha, so their textures' alpha
+channels (often gloss or leftover masks) don't punch holes in them.
 
 Converting a model the caches don't have yet (a big "glom" file takes a moment) happens on a few worker threads, so
 the dashboard keeps answering everything else meanwhile: the route hands the request to a worker (`Web::Defer`) and