Give a shader room to draw around the picture it wears (#69)

A shader ran only inside the rectangle of what wears it: the quad
has the size of the sprite, and outside of it no fragment runs. An
outline or a glow built with Sample texture was cut off at the
border. The issue still spoke of Filter.padding, but since #77 the
shader is no filter any more, the limit is the geometry.

- The Output node has a number Padding next to Edge: so many pixels
  of the picture per side the wearer draws beyond it. 0 is the
  default and draws as before, 256 is the most.
- The quad grows and its UVs grow with it, so the picture keeps its
  place and size. In the margin the UVs run on below 0 and above 1.
- Transparent is a fourth Edge mode: outside of the picture there
  is nothing. It is cut in the fragment (texelAt), so it needs no
  copy of the picture with an address mode of its own.
- Edge holds everywhere alike, also for Texture color, Texture
  alpha and unconnected inputs.
- Padding above 0 with Edge on Clamp puts the hint "Padding with
  Clamp smears the border" on the Output. The shader still
  compiles. A chosen Clamp and the default cannot be told apart.
- All four wearers draw the margin. A sprite counts in pixels of
  its frame, a text in its units, a particle source grows every
  particle about its centre.
- A nine-slice sprite gets a ring around its nine fields, as wide
  as so many border pixels. The fields themselves stay.
- Without a picture a pixel is one unit of the wearer's own size,
  or of the particle size.
- Particles now take the Edge mode of their shader. It had no
  effect on them before.
- An object wearing a padded shader is never culled, or its margin
  would vanish at the edge of the screen.
- The preview in the shader tab shows the margin and leaves room
  for it.
- Picking, the selection frame, the size and the collider stay with
  the rectangle without the margin.

Tests:
- Gate on melektaus-atx right before this commit: 216 files,
  3336 tests (3319 + 17), exit 0.
- e2e 28,30,31,37,41 on melektaus-atx: 178 checks, all pass.
  e2e 1-37,47,48,58 ran before the last change (no culling with
  padding): 1281 checks, all pass.
- 17 new unit tests: the compiler (padding, Transparent, the hint)
  and the geometry (quad, nine-slice ring).
- Seven new e2e checks: four at the sprite in module 28, one each
  for text, particles and nine-slice.
- 17 unit counter-probes all fail their tests. Three browser
  counter-probes fail their checks (5, 3 and 1 of them).
- Three screenshots looked at: the sprite with Clamp and margin in
  the scene, the preview in the shader tab, the text.
- The e2e sum of 1687 is counted (1680 + 7), the full suite and
  the smokes did not run.
- Not seen: the hint at the node in a picture, particles and
  nine-slice in a picture, the game view while playing, sprites
  without a picture, vector and pixel art pictures.

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

src/editor/particles/ParticlePreview.ts

@@ -9,6 +9,7 @@ import { crisp, hairline, type Size, Theme, Widget } from '../../ui';
 import { ParticleField } from '../../viewport/particles';
 import { particleLibrary } from '../../viewport/ParticleLibrary';
 import { shaderLibrary } from '../../viewport/ShaderLibrary';
+import { wornShader } from '../../viewport/shaders';
 import { textureLibrary } from '../../viewport/TextureLibrary';
 import type { EditorState } from '../state';
 
@@ -89,11 +90,12 @@ export class ParticlePreview extends Widget {
     const props = previewProps(this.asset, rows);
     const params = rows.map((row) => Number(props[row.key] ?? row.default));
     const ref = resolveTexture(this.state.project, props);
-    const texture = ref ? textureLibrary.get(ref, SHEET_EDGE) : null;
+    const shaders = shaderLibrary.source(this.state.project);
+    const texture = ref ? textureLibrary.get(ref, wornShader(props, shaders)?.edge ?? SHEET_EDGE) : null;
     // The source sits in the middle of the panel; a fountain then has room above and below it.
     const m = translation(this.w / 2, this.h / 2);
     this.field.hold(this.held);
-    this.field.wear(props, shaderLibrary.source(this.state.project));
+    this.field.wear(props, shaders, texture);
     this.field.sync(build.compiled, props, params, m, texture ?? Texture.WHITE, particleLibrary.now());
   }