feat(html_rich_text): add clickable link support

[ProjectAJ14]

Description

Adds support for clickable <a> tags with href attributes to the HtmlRichText widget, enabling interactive links with customizable styling and tap callbacks.

Changes

• Convert widget from StatelessWidget to StatefulWidget for proper gesture recognizer lifecycle management
• Add onLinkTap callback parameter that receives the URL when a link is tapped
• Parse <a href="..."> tags and extract href attributes for clickable functionality
• Apply default blue underlined styling to links (customizable via tagStyles['a'])
• Properly dispose TapGestureRecognizers to prevent memory leaks
• Add comprehensive test coverage for all link scenarios (18+ new tests)
• Update example app with interactive link demonstrations
• Update README with detailed documentation and usage examples

Screenshots/videos

(Interactive examples available in the updated example app)

Related Issues

Implements user-requested clickable link functionality for the html_rich_text package.

Additional Notes

• Links without href attributes are styled but not clickable
• Links without onLinkTap callback are styled but not clickable
• Maintains backward compatibility - no breaking changes to existing API
• Zero external dependencies added, keeping the package lightweight

[codecov]

Codecov Report

❌ Patch coverage is 92.30769% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...ackages/html_rich_text/lib/src/html_rich_text.dart	92.30%	4 Missing ⚠️

Flag	Coverage Δ
html_rich_text	93.15% <92.30%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...ackages/html_rich_text/lib/src/html_rich_text.dart	93.15% <92.30%> (ø)

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