fix: add pagination to GET /vendors endpoint

[EmeditWeb]

Problem

GET /vendors returns all vendors with no pagination or limit. With hundreds of vendors, this endpoint becomes slow.

What To Build

1. Add ?page=1&limit=20 query params
2. Add total count in response meta
3. Add validation that limit ≤ 100

Files To Touch

• src/modules/vendors/vendors.service.ts
• src/modules/vendors/vendors.controller.ts

Acceptance Criteria

• Paginated vendor list
• Default 20 per page, max 100
• Response includes total count
• Build passes

Mandatory Checks

• context/ files read
• npm run build passes
• PR references this issue