use Qt native MarkdownText for prose blocks

Stop hand-rolling markdown with regex. Qt 6 Text supports
textFormat: Text.MarkdownText natively — handles backticks,
bold, italic, links, lists correctly. Code blocks and diffs
still use our custom KSyntaxHighlighting rendering.

gui/main.qml

@@ -519,17 +519,7 @@ ApplicationWindow {
 
     // --- Chat block delegates ---
 
-    function linkifyPaths(text) {
+
-        // Escape HTML entities first
-        let escaped = text.replace(/&/g, '&amp;').replace(/</g, '&lt;').replace(/>/g, '&gt;')
-        // Inline code: `text` → monospace styled span
-        escaped = escaped.replace(/`([^`\n]+)`/g, '<code style="font-family:monospace;background:rgba(128,128,128,0.15);padding:1px 4px;border-radius:3px;">$1</code>')
-        // Convert newlines to <br>
-        escaped = escaped.replace(/\n/g, '<br>')
-        // Match /absolute/path or /absolute/path:line
-        escaped = escaped.replace(/(\/[\w\-.\/]+(?::\d+)?)/g, '<a href="file://$1">$1</a>')
-        return escaped
-    }
 
     Component {
         id: userDelegate
@@ -702,12 +692,12 @@ ApplicationWindow {
         id: proseSubDelegate
         Text {
             width: parent ? parent.width : implicitWidth
-            text: root.linkifyPaths(subBlock.content)
+            text: subBlock.content || ""
             wrapMode: Text.Wrap
-            textFormat: Text.RichText
+            textFormat: Text.MarkdownText
             color: palette.text
             font.pixelSize: Qt.application.font.pixelSize
-            lineHeight: 1.4
+            lineHeight: 1.3
             onLinkActivated: function(link) {
                 Qt.openUrlExternally(link)
             }