Refactor: Replace deprecated Flutter APIs across the project

[Satyanarayana001]

The project currently uses several deprecated Flutter APIs that generate warnings during analysis.

Examples include:

• withOpacity() → deprecated, should use withValues(alpha: ...)
• surfaceVariant → replaced by surfaceContainerHighest
• Deprecated drag callbacks (onAccept, onWillAccept)
• Deprecated speech recognition parameters

These deprecations may lead to compatibility issues with newer Flutter versions.

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🎯 Proposed Changes

• Replace all usages of withOpacity() with withValues(alpha: ...)
• Update surfaceVariant to surfaceContainerHighest
• Migrate deprecated drag-and-drop callbacks
• Update speech recognition API usage

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✅ Benefits

• Reduces analyzer warnings
• Improves codebase maintainability
• Ensures compatibility with latest Flutter versions

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📊 Additional Context

Running flutter analyze shows multiple deprecation warnings across different modules. :contentReference[oaicite:0]{index=0}

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🙋‍♂️ Contribution

I would like to work on this issue.

[Satyanarayana001]

I have identified multiple occurrences and will submit a PR addressing these changes soon.