refactor: Refactor feature browser, move to top-left, and increase font size

Co-authored-by: aider (gemini/gemini-2.5-pro) <aider@aider.chat>

src/FeatureBrowser.h

@@ -0,0 +1,19 @@
+#ifndef FEATUREBROWSER_H
+#define FEATUREBROWSER_H
+
+class QPainter;
+class Document;
+
+class FeatureBrowser
+{
+public:
+    FeatureBrowser();
+
+    void setDocument(Document* document);
+    void paint(QPainter& painter, int viewportWidth, int viewportHeight);
+
+private:
+    Document* m_document = nullptr;
+};
+
+#endif // FEATUREBROWSER_H