Develop every raw through the AI denoise by default, with a strength, cached

The learned demosaic was an option under Detail, off by default. It is
now how a Bayer raw is developed: on by default at full strength on
every device — which hardware runs it is the inference engine's choice
— and first in the Adjust panel, since it decides what every control
below is applied to.

Strength (0-100, default 100) replaces Keep grain: grain = 100 -
strength, the same luminance-only blend, so moving it is one GPU pass
and never a re-run. 0.21.0's sidecars stored grain; it is still read,
as the inverse, and never written.

With it on for every photograph, the result is now kept on disk
(denoise.md §7.1, §12): the network's output as half floats, keyed on
a SHA-256 of the file's bytes and the model, oldest first past a 5 GB
budget, beside the inference engine's cache. A reopened photograph and
an export of one already developed read it back instead of running the
network again; a damaged entry is a miss.

ui/dr-ui/src/labels.rs

@@ -223,7 +223,9 @@ fn catalogued(key: &str) -> Option<&'static str> {
         // panel under its own name — see `rows_filtered`.
         "param.lens_profile.apply" => "Apply",
         "param.learned_denoise.apply" => "Apply",
-        "param.learned_denoise.grain" => "Keep grain",
+        // How strongly: 100 % is the network's result, and less puts the
+        // removed noise's brightness back as grain.
+        "param.learned_denoise.strength" => "Strength",
         "param.camera_profile.apply" => "Use Profile",
         // The LookTable's strength.
         "param.camera_profile.look" => "Look Amount",