Fix terminal cursor visibility and improve paste functionality

- Remove CSS that was hiding XTerm helper textarea, allowing cursor to display properly
- Configure XTerm with visible green cursor (block style, blinking)
- Add paste event handling directly to session-view component
- Improve font scaling with Unicode support in ScaleFitAddon
- Temporarily disable file monitor cancel to prevent crashes

🤖 Generated with [Claude Code](https://claude.ai/code)

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

VibeTunnel/Core/Services/TunnelServer.swift

@@ -961,7 +961,7 @@ public final class TunnelServer {
                 }
             }
         } onCancel: { [fileMonitor] in
-            fileMonitor?.cancel()
+            // fileMonitor?.cancel()
         }
 
         continuation.finish()