fix(process manager): apply limit and offset in get_jobs

[C1-BA-B1-F3]

Summary

The PostgreSQL and MongoDB process managers ignored the limit and offset parameters in get_jobs, returning all jobs regardless of the query string. The TinyDB manager already applied both correctly.

This PR adds offset then limit to both backends, matching the TinyDB behaviour.

Changes

• pygeoapi/process/manager/postgresql.py: add .offset() / .limit() to the SQLAlchemy query
• pygeoapi/process/manager/mongodb_.py: add .skip() / .limit() to the PyMongo cursor

Test plan

• pytest tests/manager/test_manager.py — 4/4 pass
• pytest tests/manager/test_tinydb_manager_for_parallel_requests.py — 1/1 pass
• PostgreSQL integration tests require a live database and were not run locally; the change is confined to the query builder and mirrors the existing TinyDB pattern.

Fixes #2426

[C1-BA-B1-F3]

The Build failure is in test_describe_collections (assert 9 == 10) and test_get_collection_edr_query (HTTP 500), both of which also fail on the current master branch (see the 2026-09-29 templating branch run). These are pre-existing upstream regressions unrelated to this process-manager change.

The two failing tests exercise /collections and EDR queries; this PR only touches pygeoapi/process/manager/postgresql.py and pygeoapi/process/manager/mongodb_.py (the get_jobs methods). No collection or EDR code is modified.

Happy to rebase once upstream fixes the CI environment.