Develop the film last, in the view transform's place

A film stock ran at order 25, after white balance and exposure, and
everything after it — contrast, the curves, the colour mixer, the
grading, every mask layer's tone — acted on the film's display-referred
output, as though the frame had been scanned and then worked on. That
was a display-referred rendering in the middle of the chain, which D19
removes (FR-DEV-3f, FR-DEV-3j).

`film_sim` is now in `Stage::View` beside `view_transform`. While a
stock is loaded the composer emits it in the view transform's place and
not the sigmoid; otherwise the sigmoid. So every edit is a decision
about the exposure the negative receives, and the film is the last
thing that happens to the picture — after the detail stage too, in the
view pass, which already binds the film's tables, the mask array and
the grain's source position. Its per-layer settings blend there as they
did in the fused pass.

`op_renders` goes: a rendering is chosen, not suppressed, and the only
render with no view transform is the camera-space tap. The YAML order
moves to 190 so the panel reads in pipeline order; the stage, not the
number, is what places it.

Existing edits that combine a stock with tone or colour operations now
render differently: those operations used to act on the print, and now
act on the scene.

core/dr-pipeline/src/lib.rs

@@ -176,7 +176,14 @@ mod tests {
                 assert!(!shader.source.contains("---- view_transform ----"));
                 continue;
             }
-            let point = shader.source.contains(&format!("---- {id} ----"));
+            // A view operation is in the view pass when a detail stage
+            // follows, which it does here (D19).
+            let block = format!("---- {id} ----");
+            let point = shader.source.contains(&block)
+                || shader
+                    .view
+                    .as_ref()
+                    .is_some_and(|v| v.source.contains(&block));
             let neighbourhood = detail
                 .passes
                 .iter()
@@ -189,8 +196,12 @@ mod tests {
             );
             fused_blocks += usize::from(point);
         }
+        let view_blocks = shader
+            .view
+            .as_ref()
+            .map_or(0, |v| v.source.matches("---- ").count());
         assert_eq!(
-            shader.source.matches("---- ").count(),
+            shader.source.matches("---- ").count() + view_blocks,
             fused_blocks,
             "the fused shader carries a block nothing in the chain asked for"
         );