Fix #316: the section eye switches off Light, Color and Detail too

The pipeline honoured a section's eye only where it applies Effects,
Optics, Geometry and Calibration, so turning the eye off on Light, Color
or Detail changed nothing. DevelopSettings::effective() resets the
switched-off sections to their defaults (Light with the tone curve; Color
with white balance, mixers, grading and point colour; Detail), and both the
CPU and GPU renderers render those. Borrowed, so free, when every section
is on.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01912WaK6Rmew3wxZuPyX7E8

crates/develop/src/lib.rs

@@ -68,6 +68,32 @@ impl DevelopSettings {
         !self.disabled_sections.iter().any(|s| s == section)
     }
 
+    /// The settings as rendered: an Edit-panel section whose eye is off contributes nothing (issue
+    /// #316). Light (with its tone curve), Color (white balance, presence, the mixers, colour grading
+    /// and point colour) and Detail are reset to their defaults here; Effects, Optics, Geometry and
+    /// Calibration the pipeline switches off where it applies them. Borrowed when every section is on.
+    pub fn effective(&self) -> std::borrow::Cow<'_, DevelopSettings> {
+        let off = |section: &str| !self.section_enabled(section);
+        if !(off("light") || off("color") || off("detail")) {
+            return std::borrow::Cow::Borrowed(self);
+        }
+        let mut d = self.clone();
+        if off("light") {
+            d.reset_section(Section::Light);
+            d.reset_section(Section::Curve);
+        }
+        if off("color") {
+            for section in [Section::Color, Section::Mixer, Section::BwMix, Section::Grading, Section::PointColor] {
+                d.reset_section(section);
+            }
+            d.point_colors.clear();
+        }
+        if off("detail") {
+            d.reset_section(Section::Detail);
+        }
+        std::borrow::Cow::Owned(d)
+    }
+
     pub fn set_section_enabled(&mut self, section: &str, on: bool) {
         self.disabled_sections.retain(|s| s != section);
         if !on {