WIP: clarity and texture

Checkpoint committed by the coordinator, not by the authoring agent: the
session hit its API limit mid-task and left this work uncommitted. Committed
so it survives, NOT because it is finished - expect failing tests and
half-applied changes. The agent resumes from here.

core/dr-pipeline/ops/texture.yaml

@@ -0,0 +1,23 @@
+# A hand-written node — see `clarity.yaml`, whose implementation this shares.
+id: texture
+order: 130
+
+attributes: [detail]
+rust: Texture
+
+why_rust: |
+  The same neighbourhood operation as clarity, at a tenth of the scale: one
+  implementation in `src/ops/local_contrast.rs`, parameterised by the band it
+  acts on. Two nodes rather than one node with two sliders because the radius
+  is the *definition* of each control rather than a setting of it, and because
+  a texture at zero must then cost nothing at all — which `is_active()` gives
+  for free and a merged node would have had to hand-write.
+
+placement: |
+  Immediately after clarity, and for the same reasons: after noise reduction,
+  which must not be handed amplified grain, and before capture sharpening,
+  which belongs last.
+
+  After clarity specifically, so that the fine base is computed on the
+  modelling the coarse control has already settled rather than the other way
+  round.