docs: fix misleading README claims, add missing features, remove hr noise

- Fix "server does not start by default" (MCP now auto-starts)
- Rephrase tagline to name ReClass.NET/ReClassEx directly
- Add missing features: enums, bitfields, PDB import, themes, disasm preview, heatmap, MDI tabs, import/export
- Note Qt 5 support alongside Qt 6
- Align autoStartMcp default to true in options dialog
- Remove all horizontal rule separators

src/optionsdialog.h

@@ -16,7 +16,7 @@ struct OptionsResult {
     bool    menuBarTitleCase = true;
     bool    showIcon = false;
     bool    safeMode = false;
-    bool    autoStartMcp = false;
+    bool    autoStartMcp = true;
     int     refreshMs = 660;
 };