Add automated security scanning pipeline with Slither and Mythril

[Smartdevs17]

Description

No automated security scanning for Solidity/EVM contracts. Integrate Slither and Mythril in CI pipeline.

Acceptance Criteria

• Slither integration with all detectors enabled
• Mythril symbolic execution in CI
• Vulnerability severity classification
• CI gate on medium+ severity findings
• Historical finding tracking
• False positive suppression mechanism

Technical Scope

• .github/workflows/security-audit.yml
• contracts/evm/
• Edge: tool version drift, analysis timeout on large contracts, false positive management

[OlaBakare]

@OlaBakare has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hi, I'd love to work on this issue. I can handle this issue.
Thank you.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @OlaBakare to this issue.

[coderolisa]

@coderolisa has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hello maintainer I've reviewed this issue and would like to work on it
please assign

ℹ️ Repo Maintainers: To accept this application, review their application or assign @coderolisa to this issue.

[OTimileyin]

@OTimileyin has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I would like to apply for this issue, I am currently working on something familiar with this.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @OTimileyin to this issue.

[JoaquinSkorg]

@JoaquinSkorg has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

Hello Maintainer, kindly assign this issue to me

ℹ️ Repo Maintainers: To accept this application, review their application or assign @JoaquinSkorg to this issue.