feat: Add critical security enhancements

[cjcsecurity]

• Add CodeQL security scanning workflow
• Add dependency review workflow
• Add security scan workflow (npm audit + manifest validation)
• Add Content Security Policy to manifest.json
• Add security setup instructions

These changes implement automated security scanning, dependency vulnerability checking, and CSP protection for the browser extension.

Description

Related Issue (if applicable)

Fixes #

Type of Change (check all that apply)

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

Security Considerations (if applicable)

Testing Performed (check all that apply)

• Manual testing in Chrome
• Verified all existing features still work correctly
• Tested with different types of indicators (IPs, hashes, domains)

Checklist (check all that apply)

• My code follows the code style of this project
• I have updated the documentation accordingly (if needed)
• My changes do not introduce any security vulnerabilities
• I understand that my PR may need modifications to meet requirements

Screenshots (if applicable)