feat(source): add deterministic fieldops fixture api

[jaeyeopme]

Motivation

Add the deterministic source data and local fixture API needed before mapping and validation work starts.

Scope

• Add FieldOps Desk job and job update fixture files.
• Add a local source API for date-range filtering, pagination, and related job updates.
• Add tests that lock fixture counts, record types, pagination, and filtering behavior.
• Expand CI so the full test suite and coverage gate run on this PR branch.

Out of Scope

• Mapping source records into clean output rows.
• Validation and duplicate handling rules.
• Report writing.
• SQLite run history.
• API or CLI export behavior.

Modifications

• Add source job records with valid, invalid, duplicate, and out-of-range cases.
• Add related job update records used by later workflow steps.
• Add a typed source API that returns fixture-order pages and filters updates by requested job ids.
• Add failure checks for invalid pagination and malformed fixture files.

Test Plan

• uv run pytest tests/test_sample_data.py tests/test_source_api.py -v
• uv run ruff check sample_data src tests
• uv run basedpyright
• uv run pytest tests/test_source_api.py --cov=clean_data_export_api.source_api --cov-report=term-missing
• uv run pytest -v
• uv run pytest --cov=clean_data_export_api --cov-report=term-missing --cov-fail-under=90
• uv run python -m compileall src tests

Docs Impact

none

ADR Check

• No architecture or scope decision needs a new or updated ADR.

Result

The demo date range returns exactly 9 source jobs, pagination is deterministic, and related updates are returned only for requested job ids.