test: add integration test suite for data redaction and validation in…

[extolkom]

closes #280

Summary
While several retention tests existed, there was no focused coverage proving that dry-run never mutates data and that only declared piiFields are redacted. This PR adds that coverage across two test files.
Changes
tests/retention.dryRun.test.js

dryRun: true produces zero writes — seeds rows into the retention table, runs the job with dryRun: true, asserts no rows were deleted or modified, and confirms the returned report contains the expected candidate count
dryRun report includes candidate rows without touching them — verifies the report lists affected row IDs while the actual table rows remain intact after the run
dryRun: false mutates data — confirms the non-dry path does delete/redact, proving the dry-run guard is the only difference between the two modes

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[extolkom]

CI failures are pre-existing — both Lint and Test jobs fail with npm error notarget No matching version found for c8@^11.1.0, a broken dependency in package.json unrelated to this PR. No files outside tests/retention.dryRun.test.js and tests/retention.unit.test.js were modified.

[mikewheeleer]

clean diff — merging this 🙌