[husthunterpy01]

What

A Seniority filter on Find Jobs, next to Category and Country. The API already accepted ?seniority_level=; this adds the missing dropdown and an endpoint to fill it.

Backend

• GET /api/v1/jobs/seniority-levels lists the levels that currently have jobs with their counts, lowest level first (jobs without a level are left out). It mirrors GET /jobs/countries and is declared before /{job_id}.
• The seniority_level parameter's description points to it.
• Documented in document/backend/SILVER_SYNC.md.

Frontend

• A Seniority dropdown in the filter row, built from the new endpoint so it only offers levels that have jobs, with counts (for example "Senior (365)").
• It follows the other filters: a pick only takes effect on Apply, Clear and Clear filters reset it, it is kept in the URL (?seniority=3) so a filtered list can be shared or reloaded, and a level that no longer has jobs is dropped from a stale link.
• Level 2 is labelled "Mid-level or not stated", because jobs whose title says nothing about level are stored as mid-level (see "Default level" in SILVER_SYNC.md). The filter matches one exact level, not "and above".
• If the levels cannot be loaded, the page still works with just "All levels".

Testing

• Backend: ruff clean, 336 tests pass, including 7 new ones for the filter (each level, mid-level for unmarked titles, combined with other filters, invalid values, the endpoint, and that it is not swallowed by /{job_id}).
• Frontend: format, lint, type-check and build pass; 96 node and 112 component tests pass (new ones for the option list, URL state, Apply/Clear and the service calls); 19 Playwright tests pass (3 new), stable over 8 repeats.
• Checked against the real backend and a real browser on a throwaway database with seeded jobs: the dropdown is filled from the real endpoint, picking Senior returns exactly the senior jobs, the URL becomes ?seniority=3, and a reload keeps the choice. The Playwright tests use a hand-written mock API, so this run is what confirms the two sides agree.

Notes for review

• With a third dropdown, Apply and Clear wrap onto a second line at desktop widths. It reads fine; narrowing the selects would put them back on one row but would truncate the longer labels.
• Seniority comes from the job title (see the "Seniority level" section in SILVER_SYNC.md), so only the level words in a title are reliable; "Mid-level or not stated" is partly a guess.