fix: make code diffs reliably horizontally scrollable (#85)

Diff rows use maxWidth: .infinity inside a horizontal ScrollView, whose
width proposal is unspecified. The resolution against a LazyVStack's
cross-axis estimate was non-deterministic across devices: some scrolled,
others collapsed to the viewport width and clipped long lines with no way
to scroll. Give the content a definite intrinsic width via fixedSize so
horizontal scrolling works on every device.

Reviewed-on: https://codeberg.org/secana/Forji/pulls/88

Forji/Forji/Views/DiffView.swift

@@ -23,6 +23,12 @@ struct DiffView: View {
 
     var body: some View {
         ScrollView(.horizontal) {
+            // `.fixedSize(horizontal:)` gives the content a definite intrinsic
+            // width (the widest line) inside the horizontal scroll view. Without
+            // it, the rows' `maxWidth: .infinity` resolves ambiguously against the
+            // scroll view's unspecified width proposal, so on some devices the
+            // content collapses to the viewport width, clipping long lines with
+            // nothing to scroll to instead of scrolling horizontally.
             LazyVStack(alignment: .leading, spacing: 0) {
                 ForEach(Array(diff.files.enumerated()), id: \.offset) { fileIndex, file in
                     let filePath = file.newName == "/dev/null" ? file.oldName : file.newName
@@ -57,6 +63,7 @@ struct DiffView: View {
                     }
                 }
             }
+            .fixedSize(horizontal: true, vertical: false)
         }
     }