Fix pagination bounds across list endpoints

[Spycall]

Summary

Enforce validated pagination bounds and consistent defaults across users, cohorts, achievements, and recommendations list endpoints.

Changes

• Apply validated pagination DTOs with numeric, minimum, and maximum checks.
• Enforce the shared default page size of 10 and maximum page size of 100.
• Bound recommendation requests at their endpoint-specific maximum of 50.
• Return bounded paginated cohort results and pass pagination through achievement list routes.
• Update focused controller regression tests.

Validation

• pnpm run build
• pnpm run typecheck
• pnpm run lint:dto
• pnpm run format:check
• 33 focused Jest tests passed

Fixes #1302
Fixes #1303
Fixes #1304
Fixes #1305

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