Fix git clone race condition in Clone Repository dialog

[lucky7323]

Problem

The Clone Repository functionality suffered from a race condition where git clone commands were silently ignored when terminals took longer than 500ms to initialize. This led to users believing their clone operations succeeded when they actually failed.

Root Cause

The original implementation used an arbitrary 500ms setTimeout() before sending the git clone command:

window.dispatchEvent(new CustomEvent("terminal:new"));
await new Promise(r => setTimeout(r, 500)); // ❌ Race condition
window.dispatchEvent(new CustomEvent("terminal:write-active", {
  detail: { data: `git clone "${url}" "${targetDir}"\n` }
}));

If the terminal wasn't ready within exactly 500ms, the terminal:write-active event would be sent to a non-existent or inactive terminal, causing the command to be silently ignored.

Solution

Replace the arbitrary timeout with proper event-driven terminal ready detection:

• Event-driven approach: Listen for the terminal:created event from the backend
• Generous timeout: 10-second maximum wait time (vs. 500ms)
• Fallback mechanism: Secondary 1-second fallback if events are missed
• Shell escaping: Add proper argument escaping to prevent command injection
• Error handling: Proper error notifications when terminal creation fails

Technical Details

• Uses the existing terminal:created Tauri event that's already handled in TerminalsContext
• Implements proper shell argument escaping with single quotes
• Provides clear error messages to users when operations fail
• Maintains backward compatibility with existing terminal system

Testing

• Verified terminal:created event exists and is handled
• Confirmed shell escaping prevents injection attacks
• Added comprehensive error handling and user notifications
• Maintained compatibility with existing terminal workflow

This fix ensures git clone operations are reliable and provides proper feedback to users when issues occur.

Fixes #21724