Title: refactor(error-handling): centralize duplicate try/catch blocks into Express error middleware

[Satvik77777]

The same try/catch -> console.log -> res.status(500)
pattern is duplicated 20+ times across agreements.ts,
crud.ts, and mcp.ts. Several console.log statements
also expose PII (req.body, contract data) and internal
details (SQL queries, stack traces) to stdout.

This issue tracks:

1. Creating server/middleware/errorHandler.ts with
   globalErrorHandler and asyncHandler utilities
2. Refactoring all route handlers to use asyncHandler
3. Removing PII-exposing console.log statements
4. Replacing with structured non-leaking error logging