docs: improve validation rule reference using mermaid flowchart

[csmdg7]

Description

This PR successfully resolves the fragmentation of plugin metadata validation rules by appending a dedicated "Common Validation Mistakes & Troubleshooting Matrix" to the bottom of docs/plugin-validation.md.

Key additions:

• A concrete troubleshooting reference matrix linking specific syntax and schema mismatches (e.g., mixing integer ranges on string fields or unescaped regex characters) to actionable resolution steps.
• A visual execution-order reference powered by an inline Mermaid flowchart to map out exactly how the frontend validation engine prioritizes validation_type presets over custom pattern regex keys.

These updates fulfill all criteria for issue #863 by eliminating ambiguity for upcoming plugin contributors without modifying surrounding tracking configurations.

Related Issues

Closes #863

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Staged locally and verified the visual integrity of the newly implemented Mermaid script using the Markdown rendering preview tool inside VS Code.
• Cross-checked error mappings directly against the core schema expectations described in the pre-existing specification tables.

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.

[csmdg7]

Hi @utksh1,

I have updated the document, but the CRLF format doesn't get approved by the bot even though I had chosen the LF format; Otherwise, I have updated the other requirements. Please do let me know if any changes are required.

Thank you!

[utksh1]

Requesting changes. The current run fails formatting-hygiene. Please fix formatting and ensure the Mermaid addition renders cleanly in the plugin validation docs.

[csmdg7]

Hi @utksh1,

I have thoroughly debugged the line-ending discrepancies. The formatting-hygiene failures were caused by local Git configuration defaults automatically injecting Windows CRLF line endings during staging.

I have now explicitly forced core.autocrlf false and core.eol lf parameters across the local environment repository settings, stripped the cache tracking, and force-pushed the file with strict Unix LF line endings.

The file and the Mermaid diagram should now render correctly. Thank you!