docs: strengthen security disclosure process for issue #418

[samanyugoyal2010]

Expand SECURITY.md with GitHub private vulnerability reporting as the preferred channel, document scope, and cross-link CONTRIBUTING.md.

Add security reporting guidance to CONTRIBUTING.md, README community section, issue template config, and bug report template so users do not file vulnerabilities as public issues.

Pull Request Checklist

Please ensure that your PR meets the following requirements:

• I have read the CONTRIBUTING guide.
• I have updated the documentation (if applicable).
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context.

Fixes # (issue number)

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)
• This change requires a documentation update

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All committers have signed the CLA.

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Codex review

No issues found.

[samanyugoyal2010]

@HarshaNalluru this can be merged