Add comprehensive text editing mode behavior documentation

[Copilot]

This PR adds detailed documentation for Remarklet's text editing functionality, addressing the need for users to understand how the text editing features work.

Changes Made

• Created new documentation page: website/docs/1.2.x/text-editing.md with comprehensive coverage of text editing behavior
• Updated navigation: Added "Text Editing" section to the documentation sidebar
• Translated technical implementation: Converted Playwright test scenarios and code behavior into user-friendly explanations

Documentation Coverage

The new documentation explains:

Core Functionality

• Text editing modes: How Remarklet transitions between editing, text editing, dragging, and resizing modes
• Safety features: Event suppression mechanism that prevents accidental activation of buttons/links during editing
• Step-by-step workflow: Clear user interaction patterns from element selection to completion

Technical Details Made Accessible

• Event handling: How click events are suppressed while preserving original functionality
• Content editability: How elements become editable and are restored afterward
• Persistence: How changes are saved to localStorage and restored across sessions
• Change tracking: How modifications are monitored and managed

User Guidance

• Best practices: Effective usage patterns and keyboard shortcuts
• Troubleshooting: Common issues and solutions
• Browser compatibility: Supported features across different browsers

Example from Documentation

The documentation includes practical examples like this one explaining event suppression:

<button onclick="alert('Button clicked!')">Click Me</button>

With Remarklet active:

1. You can click on the button to select it for editing
2. The alert dialog will not appear because click events are suppressed
3. You can modify the button text from "Click Me" to "Save Changes"
4. When you deactivate Remarklet, the button's original functionality is restored

This directly addresses the Playwright test scenario where users can "edit element text that has a mouse event without triggering that event."

Verification

• ✅ Website builds successfully with new documentation
• ✅ Navigation sidebar includes new "Text Editing" section
• ✅ Documentation follows existing style and structure
• ✅ Content is accessible at /docs/1.2.x/text-editing

Fixes #192.

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