Connect the lens vignetting correction to the pipeline

`ops/vignetting.rs` has carried a complete descriptor, polynomial, helper
and test suite without an entry in `ops/`, so it was never in `chain()`.
It reached no photograph and no panel, and `Attribute::Optics` was an empty
category in consequence — filtered out of the tab strip for having no rows,
by a chain that had never been given its only member.

Declaring it needs the one thing the operation was written against and
which did not exist. `wgsl_body` reads `radius`, and the module claimed
"the composer publishes `radius` in the shader prologue for exactly this
reason". It did not. `sample_source` now does, in both sampling branches,
beside the `source_px` it already published for the same class of caller.

It is corner-normalised there, which is the part that is easy to leave out.
`p` spans ±0.5·aspect, so its length at the corner is 0.5·length(aspect) —
about 0.901 on a 3:2 frame, not 1. Lensfun's polynomials are fitted against
a corner radius of 1, so passing `length(p)` straight in evaluates every one
of them short of where it was measured, by a factor that changes with the
aspect ratio. It would have read as a correction that is simply too weak,
which is indistinguishable from a bad profile. Both `lens.rs` and
`framing.rs` asserted the normalisation `p` does not have; corrected.

`order: 5` puts the correction ahead of the tonal stages, and the ordering
is load-bearing rather than tidy. Recovering a corner means dividing by an
attenuation below one — about two stops for a fast prime wide open — so run
after the highlights have been rolled off and clipped, the lift has nowhere
to go and the corners posterise instead of brightening.

`layer_chain` now drops `Optics` as well as the neighbourhood operations.
A local vignetting slider would have worked, which is what makes it worth
excluding: `radius` measures from the centre of the whole photograph and a
mask cannot move the optical axis, so it would lay a frame-centred radial
ramp across the picture and multiply it by the mask. The existing exclusion
covers operations that move and do nothing; this one covers an operation
that moves and does something its name does not promise. The rule both
share is now written down.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

core/dr-pipeline/src/framing.rs

@@ -893,9 +893,16 @@ impl Framing {
     /// The WGSL mapping an output pixel to a **normalised centred** source
     /// position, ready for the warp chain.
     ///
-    /// Leaves the result in `p`: centre `(0, 0)`, `r == 1` at the corner —
-    /// exactly the space [`crate::lens`] documents, so lens correction
-    /// composes on top of this without either stage naming the other.
+    /// Leaves the result in `p`: centre `(0, 0)`, spanning `±0.5 * aspect` —
+    /// the space [`crate::lens`] documents, so lens correction composes on top
+    /// of this without either stage naming the other.
+    ///
+    /// **`p` is centred but not corner-normalised**, and this used to claim it
+    /// was. Its length at the corner is `0.5 * length(aspect)`, not 1. The
+    /// corner-normalised radius the radial corrections need is published
+    /// separately as `radius` by `operation::sample_source`, which divides by
+    /// exactly that; anything reading `length(p)` as a lens radius is off by
+    /// an aspect-dependent factor.
     ///
     /// `aspect` is left in scope alongside it, since the warp chain and the
     /// sampler both need it to return to texture coordinates.