Refactor security policy into two-tier structure

[Nitya-003]

Which issue does this PR close?

• Closes Refactor SECURITY.md for better readability and actionable reporting #1301

Rationale for this change

The previous SECURITY.md was overly dense (300+ lines), blending high-level reporting policies with low-level code implementation details. This created two major issues:

1. Critical Friction: Security researchers had to scroll extensively to find reporting instructions, which could lead to public disclosure instead of private reporting.
2. User Confusion: Including "Before Fix" code snippets in the root security file risked users accidentally implementing vulnerable patterns by skimming the document.
   By moving to a "Two-Tier" structure, we ensure the project remains "Production-Ready" and accessible for SWOC'26 contributors.

What changes are included in this PR?

1. Streamlined SECURITY.md:
   • Refactored into a concise, 1-page guide.
   • Added Safe Harbor language to protect ethical researchers.
   • Implemented a structured Vulnerability Report Template.
2. Created docs/SECURITY_IMPLEMENTATION.md:
   • Relocated all technical deep-dives (SQLi/XSS/File Upload "Before vs After" examples) to this file.
   • Preserved the "Security Hall of Fame" and testing payloads for developer reference.
3. Visual Improvements: Used GitHub-native alert blocks (> [!IMPORTANT]) to highlight the private disclosure requirement.

Are these changes tested?

Documentation-only changes. I have verified:
* All internal links between SECURITY.md and docs/SECURITY_IMPLEMENTATION.md are functional.
* Mermaid diagrams and Markdown formatting render correctly in GitHub preview.

Are there any user-facing changes?

Yes. Users looking for the technical security breakdown will now find it in the docs/ folder instead of the root SECURITY.md. The root file now serves exclusively as a security policy and reporting guide.

SWOC'26

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[github-actions]

Thanks for creating a PR for your Issue! ☺️

We'll review it as soon as possible.
In the meantime, please double-check the file changes and ensure that all commits are accurate.

If there are any unresolved review comments, feel free to resolve them. 🙌🏼

[github-actions]

🎉 Congrats @Nitya-003 on getting your PR merged! 🙌
Thanks for the contribution — looking forward to more from you 🚀