Feat: MCP Gateway

[Br0wnHammer]

Describe your changes

• Add MCP Gateway to the AI Gateway — a reverse proxy that governs agent-tool interactions via the Model Context Protocol, enforcing authentication (agent keys), tool-level access control, runtime guardrails (PII, prompt injection, circuit breakers), and audit logging
• Build 6 frontend pages (Agent Keys, Servers, Tool Catalog, Audit Log, Approvals, Guardrails) with collapsible sidebar section, stat cards, charts, and paginated log viewer
• Extract shared utilities (Redis connection, rate limiter, ACL matcher, status colors) to eliminate duplication across LLM proxy and MCP Gateway code paths
• Add 30-day audit log retention cleanup endpoint and proper backend pagination with total counts

Fixes #3657

Please ensure all items are checked off before requesting a review:

• I deployed the code locally.
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• I have included the issue # in the PR.
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• The issue I am working on is assigned to me.
• I have avoided using hardcoded values to ensure scalability and maintain consistency across the application.
• I have ensured that font sizes, color choices, and other UI elements are referenced from the theme.
• My pull request is focused and addresses a single, specific feature.
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[MuhammadKhalilzadeh]

Thanks @Br0wnHammer
Code-wise things are fine.
We only need a little bit of testing the frontend pages