Finish the migration: all 65 scenes on the identity artifacts

Two helpers made the bulk of it mechanical. `inkStroke` is a drop-in for
sigEdge — the same line at the identity's weight rather than the track's — and
`castForm` is a drop-in for sigForm, same signature so call sites do not change
shape. With those in place the substitution table is one-to-one:

    sigForm(  -> castForm(     sigShape( -> castMain(     sigEdge( -> inkStroke(

Forty-seven scenes went through that pass in one run: twenty-six take the cast
and the ink, twenty-one take the ink alone. Then the gate ran over all sixty-five
and found three the pass had broken, which is the entire reason it exists.

Spectrum Sculpture rendered pure black. It had been using sigShape as a RADIAL
METRIC rather than drawing it, and the cast carries notches and a hollow — an
annulus used as a radius turns a sculpture inside out. Reverted to sigShape and
dropped to ink only. The lesson generalises: a scene that reads a form as
geometry is not a scene that draws it, and the classifier cannot tell those
apart from the source.

Eclipse Field stopped honouring its `style` trait. It opts out of surface grain,
so sigEdge was its only style evidence, and the ink replaced it. The trait claim
is now dropped — and so is the lint change that had let inkMask count as style
evidence, which was wrong and was hiding exactly this. A trait is a property of
the track a scene may honour; an artifact is content it draws. Taking the ink
says nothing about whether a scene responds to u_sigLine.

Circuit Bloom went empty at the bottom of its `grown` range, where the pads were
carried by a hairline and the ink's stroke is thinner than the edge it replaced.
Now filled as well as stroked.

Also: the backtick check now covers every shader literal rather than only the
preamble, because a mechanical pass over sixty files reintroduced one
immediately. Three rounds lost to that typo is enough.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

flow-state/src/scenes/shader/gate-corridor.js

@@ -16,6 +16,7 @@ export const gateCorridor = {
     kind: 'fragment',
     // Takes the track's surface grain, but lightly — this is drawn, not filmed.
     texture: 0.4,
+    consumes: ['cast', 'ink'],
     traits: ['shape', 'camera', 'space', 'style'],
 
     params: {
@@ -62,7 +63,7 @@ vec4 scene(vec2 uv, vec2 p) {
         float phase = fract((fi / float(u_gates)) + t);
         float scale = u_aperture * exp(phase * 3.2) * 0.35;
 
-        float d = abs(sigShape(q / max(scale, 1e-3)) * max(scale, 1e-3));
+        float d = abs(castMain(q / max(scale, 1e-3)) * max(scale, 1e-3));
 
         // Near gates are drawn thicker and brighter: the only depth cue that
         // matters once the geometry is right.
@@ -83,7 +84,7 @@ vec4 scene(vec2 uv, vec2 p) {
 
     col = sigAir(col, p, 1.0 - smoothstep(0.0, 1.2, length(q)));
     col += sigGrain(uv);
-    return vec4(col, 1.0);
+    return vec4(inkValue(col), 1.0);
 }
 `,
 };