Fix assistant message text truncating with "…" instead of wrapping

Two contributing layout issues in the chat message bubble:

1. MessageRow's content VStack (icon + text HStack) had no
   .frame(maxWidth: .infinity), so it sized to its content's ideal
   width instead of the space actually available.

2. swift-markdown-ui renders paragraphs with mixed inline styling
   (bold/italic runs next to plain text) as concatenated Text(+)
   segments, which on macOS report their ideal unwrapped single-line
   size for height purposes instead of wrapping — truncating with "…"
   regardless of window width. Plain single-style paragraphs (a single
   Text) weren't affected, which is why some lines wrapped fine and
   others didn't.

Fixed by adding .frame(maxWidth: .infinity, alignment: .leading) to
the MessageRow content stack, and .fixedSize(horizontal: false,
vertical: true) to the markdown paragraph label so height is
recomputed for the width actually given instead of the ideal width.

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

oAI/Views/Main/MarkdownContentView.swift

@@ -61,8 +61,15 @@ struct MarkdownContentView: View {
             .markdownBlockStyle(\.paragraph) { configuration in
                 configuration.label
                     .markdownMargin(top: 0, bottom: 8)
+                    // MarkdownUI builds mixed-style paragraphs (bold/italic runs alongside
+                    // plain text) as concatenated Text(+) segments, which on macOS report
+                    // their ideal (unwrapped, single-line) size instead of wrapping to the
+                    // width actually available — truncating with "…" mid-word. Forcing the
+                    // height to be recomputed for the given (flexible) width fixes it.
+                    .fixedSize(horizontal: false, vertical: true)
             }
             .textSelection(.enabled)
+            .frame(maxWidth: .infinity, alignment: .leading)
     }
 
     // MARK: - Parsing

oAI/Views/Main/MessageRow.swift

@@ -185,6 +185,7 @@ struct MessageRow: View {
                     .foregroundColor(.oaiSecondary)
                 }
             }
+            .frame(maxWidth: .infinity, alignment: .leading)
         }
         .padding(16)
         .background(Color.messageBackground(for: message.role))