Auto-select timestamp text in TTD navigation dialog

[Copilot]

Problem

When the "Navigate to TTD Timestamp" dialog opens, the current timestamp is displayed in the input field but not selected. This requires users to manually select the text before they can:

• Copy the current timestamp to clipboard
• Paste a new timestamp to navigate to

This creates unnecessary friction in a common workflow when working with Time Travel Debugging (TTD).

Solution

Added a call to selectAll() on the timestamp QLineEdit field after populating it with the current TTD position. This automatically selects/highlights the text when the dialog opens.

Changes

Modified: ui/timestampnavigationdialog.cpp

In the initializePositions() method, after setting the text:

m_timestampEdit->setText(positionText.toUpper());
m_timestampEdit->selectAll();  // Select text for easy copy/paste

User Experience Improvement

Before:

• Dialog opens showing "13900:1DAC" with cursor at end
• User must triple-click or drag to select text
• Then can copy or paste

After:

• Dialog opens with "13900:1DAC" already selected
• Immediate Ctrl+C to copy current position
• Immediate Ctrl+V to paste and replace with new position
• Immediate typing to replace with new value

This follows standard UI patterns where pre-populated dialog fields have their content selected by default, making them immediately ready for user action.

Testing

The change follows Qt's standard QLineEdit API and patterns used throughout Qt applications. No additional testing infrastructure is required for this UI enhancement.

Fixes the issue reported in #[issue_number] where @xusheng6 requested this functionality improvement.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Navigate to TTD Timestamp dialog should have the current timestamp selected by default</issue_title>
<issue_description>So that I can directly paste a new one into it, or copy the current one</issue_description>

Comments on the Issue (you are @copilot in this section)

@xusheng6

Fixes #870

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