docs: update documents for sanity check

[ktro2828]

What

This pull request enhances the documentation for the sanity checking functionality, improves clarity in the CLI documentation, and standardizes rule severity levels across the schema requirements. The most significant changes include the addition of a dedicated tutorial for sanity checks, a new API reference section for the sanity module, detailed explanations of CLI outputs and exit codes, and normalization of severity naming conventions.

Documentation Additions and Improvements:

• Added a new tutorial (sanity.md) that explains how to use the sanity_check function, display results, save outputs, and implement custom checkers. This makes it easier for users to understand and extend sanity checks.
• Introduced a new API reference section for t4_devkit.sanity, including filtering options and improved navigation in the documentation. [1] [2]
• Updated the CLI documentation for t4sanity to explain exit status logic, provide a detailed description of the JSON output format, and clarify result table columns. [1] [2]

Schema Documentation Standardization:

• Standardized all rule severity labels in requirement.md to uppercase (ERROR, WARNING) for consistency across documentation.

Navigation and Organization:

• Updated the documentation navigation (mkdocs.yaml) to include the new tutorial and API reference for sanity, improving discoverability.
• Removed a duplicate or misplaced reference to t4_devkit.common.sanity in the common API documentation for clarity.

[Copilot]

Pull Request Overview

This PR enhances the documentation for the sanity checking functionality by adding comprehensive tutorials and API references, improving CLI documentation clarity, and standardizing severity level naming conventions across schema requirements.

Key Changes:

• Added a new sanity check tutorial with usage examples and instructions for implementing custom checkers
• Enhanced CLI documentation with detailed exit status logic, JSON output format descriptions, and result table explanations
• Standardized all severity levels to uppercase (ERROR, WARNING) throughout schema documentation

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
mkdocs.yaml	Added navigation entries for the new sanity tutorial and API reference
docs/tutorials/sanity.md	New tutorial documenting sanity check usage and custom checker implementation
docs/schema/requirement.md	Standardized severity level casing from mixed case to uppercase
docs/cli/t4sanity.md	Enhanced with exit status logic table and JSON format field descriptions
docs/apis/sanity.md	New API reference page for the sanity module with filtering options
docs/apis/common.md	Removed duplicate sanity reference from common API documentation

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