feat: update default AI model from Claude 3.5 to Claude 4.5 Sonnet across codebase

[shivasurya]

This pull request updates SecureFlow to use the new Anthropic Claude 4.5 Sonnet AI model (claude-sonnet-4-5-20250929) as the default for security analysis, deprecating the previous default (claude-3-5-sonnet-20241022). The changes ensure the new model is available throughout the CLI, extension, configuration, and documentation, and provide clear guidance and warnings to users about the transition.

Model selection and default behavior:

• Changed the default AI model from claude-3-5-sonnet-20241022 to claude-sonnet-4-5-20250929 across all configuration files, CLI commands, TypeScript/JavaScript classes, and onboarding flows. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Model support and configuration:

• Added claude-sonnet-4-5-20250929 to supported model lists, enums, and type definitions in config and source files. Updated context window and output token limits for the new model. [1] [2] [3] [4] [5] [6]

Deprecation handling and user messaging:

• Marked claude-3-5-sonnet-20241022 as deprecated in configuration, documentation, and UI, recommending users switch to Claude 4.5. Added runtime warnings in the CLI when the deprecated model is used. [1] [2] [3] [4] [5] [6]

Documentation and UI updates:

• Updated CLI and extension documentation, onboarding screens, and model selection dropdowns to reflect the new recommended model and deprecation status of the old model. [1] [2] [3]

Internal logic and client support:

• Updated the AI client factory and Claude client logic to support the new model, ensuring all relevant code paths recognize and use claude-sonnet-4-5-20250929 as the preferred option. [1] [2] [3] [4]

These changes help ensure SecureFlow users benefit from the latest model capabilities, while providing clear guidance and compatibility for existing workflows.