Reduce redundant deployments requests on deployments page

[jeevan6996]

closes #20397

this PR removes a redundant deployments request in the deployments route by relying on paginated response metadata for empty-state/count handling.

Changes

• stop issuing a separate count query in ui-v2/src/routes/deployments/index.tsx
• keep existing empty-state UX by deriving state from paginated count plus active filters
• extract route-level filter/pagination helpers into ui-v2/src/routes/deployments/utils.ts
• add tests for helper behavior in ui-v2/src/routes/deployments/utils.test.ts

Testing

• attempted: npm run test -- src/routes/deployments/utils.test.ts
• local environment failure: Node dynamic library load error (libsimdjson.31.dylib missing)