refactor: labeled dropdown's tab is a plain carve-out — the section idiom

The wide label-carrying slope was over-engineered; the label now sits in a
flat recessed tab exactly like a section title's: top/right/left walls at
the ring's own depth, bottom open into the trigger's groove ring, the
ring's top wall picking up right of the tab's throat. Three prims instead
of five, and the same visual language as the params pane's sections.

Co-Authored-By: Claude Fable 5 <[email protected]>

 src/widget/input/dropdown.rs | 47 +++++++++++---------------------------------
 1 file changed, 12 insertions(+), 35 deletions(-)

diff --git a/src/widget/input/dropdown.rs b/src/widget/input/dropdown.rs
index 5020c4d..90bfe0d 100644
--- a/src/widget/input/dropdown.rs
+++ b/src/widget/input/dropdown.rs
@@ -328,19 +328,15 @@ impl Dropdown {
             let face = if raw_bg[3] > 0.001 { bg_color } else { [0.0; 4] };
             let strip = self.label_top();
             if strip > 0.0 {
-                // Labeled: the inset grows a label-width TAB (the section-
-                // title-tab idiom) — only where the label text runs does the
-                // top wall rise over the strip, widening into a long
-                // descending slope the label sits on (its inward half spans
-                // the whole strip, ending at the trigger's top edge where the
-                // lip's bevel rises back up). Right of the tab the ring keeps
-                // its normal top wall. Composed from edge-suppressed pieces,
-                // section-relief style, so walls continue across the joints.
+                // Labeled: the label sits in a CARVE-OUT tab, the section-
+                // title idiom — a flat recessed well hugging the label run,
+                // its bottom open into the trigger's groove ring below (the
+                // tab's walls: top, right, left). Right of the tab the ring
+                // keeps its normal top wall, starting at the tab's throat.
                 let g = depth * 0.5;
                 let orad = (r4[0] + g, r4[1] + g, r4[2] + g, r4[3] + g);
                 let (outer_x, outer_r) = (x - g, x + w + g);
                 let (tab_top, ring_top) = (y - strip - g, y - g);
-                let bottom = y + visual_h + g;
                 // The tab hugs the label run (drawn at x + inset): text width
                 // plus the inset each side, kept inside the trigger's span.
                 let (fam, fsize) = crate::layout::control_label_font_detached_parsed();
@@ -355,6 +351,13 @@ impl Dropdown {
                     .min(outer_r - outer_x);
                 let tab_r = outer_x + tab_w;
 
+                // The tab: bottom open into the ring.
+                ctx.recess_edges(
+                    Rect { x: outer_x, y: tab_top, width: tab_w, height: ring_top - tab_top },
+                    (orad.0, orad.1.min(strip * 0.5), 0.0, 0.0),
+                    depth,
+                    (true, true, false, true),
+                );
                 // The ring proper: right + bottom + left walls, one prim so
                 // its corners blend internally.
                 ctx.recess_edges(
@@ -372,32 +375,6 @@ impl Dropdown {
                         (true, false, false, false),
                     );
                 }
-                // Tab side walls, continuing the ring's left wall up to the
-                // tab's top corner and closing its right side.
-                ctx.recess_edges(
-                    Rect { x: outer_x, y: tab_top, width: tab_w, height: strip },
-                    (orad.0, orad.1.min(strip * 0.5), 0.0, 0.0),
-                    depth,
-                    (false, true, false, true),
-                );
-                // The wide top slope, tab width only. The slope profile
-                // straddles its boundary by ±roll/2, so the boundary sits at
-                // the MIDPOINT of the run it covers — the tab's top edge down
-                // to the trigger's top — or the outward half would climb past
-                // the inset into whatever sits above (it washed into the
-                // ramp's graph; found the hard way).
-                let span = strip + g;
-                ctx.recess_edges(
-                    Rect {
-                        x: outer_x,
-                        y: tab_top + span * 0.5,
-                        width: tab_w,
-                        height: bottom - (tab_top + span * 0.5),
-                    },
-                    (orad.0, orad.1.min(strip * 0.5), 0.0, 0.0),
-                    span,
-                    (true, false, false, false),
-                );
                 let rect = Rect { x, y, width: w, height: visual_h };
                 let rrad = (r4[0], r4[1], r4[2], r4[3]);
                 if face[3] > 0.001 {