fix(onboarding): profile sheet header full-bleed under keyboard (#1162)

* fix(onboarding): profile sheet header stays full-bleed under keyboard

Keyboard avoidance lays the sheet content out below the sheet's top
edge, exposing the presentation background above the lava band as a
light cap with square band corners. Bleed the band's own background
layer upward past the content edge (single paint layer, clipped by the
sheet shape) so any gap above the header reads as the band continuing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* refactor(onboarding): name the header bleed constant

Per review on #1162: replace the magic -400 with a documented
headerBleedHeight constant.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: yewreeka

Convos/Profile/ProfileSetupSheet.swift

@@ -62,6 +62,11 @@ struct ProfileSetupSheet: View {
     @State private var contentHeight: CGFloat
 
     private static let privacyAndTermsURL: String = "https://hq.convos.org/privacy-and-terms"
+    /// How far the header band's background bleeds above the content's top
+    /// edge. Only the sheet-clipped gap left by keyboard avoidance is ever
+    /// visible, so the value just needs to comfortably exceed the largest
+    /// such gap on any device; the overdraw is otherwise clipped away.
+    private static let headerBleedHeight: CGFloat = 400.0
 
     init(mode: ProfileSetupSheetMode, onSaved: (() -> Void)? = nil) {
         self.mode = mode
@@ -174,7 +179,14 @@ struct ProfileSetupSheet: View {
         // 132pt band per design: 40 above the text block, 28 below.
         .padding(.top, DesignConstants.Spacing.step10x)
         .padding(.bottom, 28.0)
-        .background(.colorLava)
+        // The negative padding bleeds the band upward, past the content's
+        // top edge; the sheet's shape clips it. Keyboard avoidance lays the
+        // content out below the sheet's top edge, which otherwise exposes
+        // the presentation background above the header. One paint layer, so
+        // there is no seam at the band's own edge.
+        .background {
+            Color.colorLava.padding(.top, -Self.headerBleedHeight)
+        }
     }
 
     private var nameRow: some View {