feat: add POLYGON_CRITERIA_STATS job handler

[ConnectedSystems]

Summary

Adds a new POLYGON_CRITERIA_STATS job type that computes histogram bins and summary statistics for criteria values inside a user-drawn polygon. This is the compute half of the polygon criteria distribution feature; the UI and infra half lives in AIMS/reefguide (branch feat/consolidated-map-ui).

Changes

• New handler (src/job_worker/handlers.jl): PolygonCriteriaStatsHandler takes a GeoJSON polygon, a region ID and a list of criteria IDs, and returns per-criteria { bins, min, max, mean, median, p5, p95, nodata_count }. Payload structs mirror the TypeScript PolygonCriteriaStatsInput / PolygonCriteriaStatsOutput schemas.
• Two-pass spatial filter: the slope table is narrowed by a cheap vectorised bbox range check first, then the expensive point-in-polygon test runs only on the reduced candidate set.
• Stuck-job fix (src/job_worker/worker.jl): if an unhandled exception occurs after a job has been claimed (e.g. an OOM kill), the job is now marked FAILED instead of sitting in IN_PROGRESS indefinitely.
• Registers the job type in __init__, adds it to .env.dist JOB_TYPES, and adds the Statistics dependency.

Deployment note

PublishDockerImage.yml only runs on release: published or manual workflow_dispatch, and the latest tag is only applied on main. Merging this alone will not update the :latest image that dev/prod consume — a release or manual dispatch from main is needed before the deployed workers will accept the new job type.

Test plan

• Submit a POLYGON_CRITERIA_STATS job against a known region and polygon; confirm bins and summary stats are returned
• Confirm criteria columns missing from the slope table are skipped with a warning rather than erroring
• Confirm an empty polygon (no reef data) returns zeroed stats rather than failing
• Confirm a job killed mid-processing transitions to FAILED

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