chore: Add modular validation system for API routes leading to integration tests

[waqasshaukat]

Purpose of this PR

1. Shared Validation Logic for Chat API Routes

2. PURPOSE OF EXTRACTION:
   The validation logic is used by BOTH:
   -Real API routes (app/api/chat/route.ts, app/api/ymax/route.ts, app/api/support/route.ts)
   -(in the subsequent PR)Test mocks (test/setup.ts - MSW handlers)

3. By extracting validation into shared functions, we ensure:

• Single source of truth for validation rules
• Tests automatically stay in sync with API changes
• If a developer changes validation logic here, both API and tests update together
• Impossible for tests to return different status codes than real API

4. ARCHITECTURE:
   Each validation concern is separated into its own function for:

• Better modularity and reusability
• Easier testing of individual validators
• Ability to compose validators based on endpoint needs
• Future extensibility (add new validators without modifying existing ones)

5. **This PR also fixes an existing but of not picking up the MCP server on the chat/[id] route if the page is hard-refreshed. Reason of doing in this PR is that while validating the correct MCP (during development) the prescribed route giving an error **

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Status	Name	Latest Commit	Preview URL	Updated (UTC)
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