Effects: Glass loads its texture from an image file

Effect › Distort › Glass… offered only its four built-in textures. The
reference app's Texture menu also has Load Texture, which takes an
image file as the glass surface.

The Glass dialog now has a Load Texture… button. It reads a PNG, JPEG,
GIF, WebP, TIFF, BMP, PSD or PSB file within the pixel allowance the
renderer draws images in, and the Texture menu gains Loaded Texture.
The effect stores the image's gray levels in `textureImage` as a
grayscale PNG in base64, so the document saves the texture with the
effect, and copies of the effect carry it. effect.apply and
effect.setParams take `textureImage` as {path}, {name, dataBase64} or
the stored string; any other value is an error.

The texture lies one image pixel per point at Scaling 100%, centered on
the object and repeated. Each pixel's luma is the surface's height,
from 0 for black to 1 pt for white, and a transparent pixel counts as
middle gray. A Glass without `textureImage` draws and saves as before.

Docs: docs/mcp.md (Glass textures), docs/effects-parity.md,
docs/gaps.md, docs/target-app-parity.md.

docs/gaps.md

@@ -202,7 +202,7 @@ from G14 and the budget run of G15: **~170–270 h** one agent, ~50–80 h wall
 ## G2 Photoshop-style raster effects and the Effect Gallery
 
 - **Missing:** 28 of 57 filters (the remaining 14 Artistic filters and all of Sketch), the Effect Gallery dialog, Load
-  Texture for Glass and Texturizer. Measured in
+  Texture for Texturizer. Measured in
   [effects-parity.md](effects-parity.md).
 - **Done:** the pixel-filter pipeline and 29 filters (Artistic: Film Grain, Blur, Brush Strokes, Distort, Pixelate, Sharpen, Stylize,
   Texture, Video), Brush Strokes on 2026-10-11, Film Grain on 2026-10-12, and Smart Blur's Edge Only and Overlay Edge