feat: add a shigola mode that purges or seeds each metatile (MAPCO-11992)

[NivGreenstein]

Question	Answer
Bug fix	✖
New feature	✔
Breaking change	✖
Deprecations	✖
Documentation	✔
Tests added	✔
Chore	✖

Related issues: MAPCO-11992. Depends on MapColonies/schemas#181.

Further information:

With app.map.provider: shigola, retiler keeps Shigola's tile cache fresh instead of rendering tiles. Each metatile job becomes one POST {app.map.url}/cache/{purge|seed} with the metatile's lng/lat bbox and its zoom as both ends of the zoom range. A seed always sends overwrite: true. No map is fetched, split or stored, and detiler is not used.

How a job ends

Response	Job
2xx	completed
400, 422 (bad bbox, unknown map, too many tiles)	cancelled, never retried
401, 403, 404, 429, 5xx, timeout, connection error	failed, retried by pg-boss

• Why cancel: pg-boss's fail() always retries while retries remain, and a fetched job has no public terminal failure. So a NonRetryableError makes the queue provider cancel the job instead.
• Deviation from the ticket: 401, 403 and 404 are retried, although the ticket says to end every 4xx except 429 without retry. They mean a token or URL mistake, which a deploy fixes, and would otherwise cancel every metatile in the meantime.

Other changes

• Processor choice: the map provider now picks the metatile processor: TileProcessor for wms and arcgis, ShigolaCacheProcessor for shigola.
• Metrics: retiler_shigola_requests_count{operation, outcome, code}, retiler_shigola_tiles_count{operation, result} and retiler_shigola_request_duration_seconds{operation, z}.
• Traces: a shigola.cache span per job.
• Helm: the token comes from the chart's Secret or an existing one (env.map.shigola.existingSecret). Tile matrix sets default to ["WorldCRS84Quad"], the grid the metatile zoom is in.
• README: a new "Shigola mode" section.

Before merging

1. Merge and release feat: add a shigola map provider in a new retiler v3 schema (MAPCO-11992) schemas#181.
2. ⚠️ Replace the temporary dependency. @map-colonies/schemas currently points at the tarball built from feat: add a shigola map provider in a new retiler v3 schema (MAPCO-11992) schemas#181, so CI can run against the new vectorRetilerV3 schema before the release. Set it back to the released version (and update the lockfile) before merging.

Testing:

• Unit tests pass (79). New cases cover every outcome class, token handling, the request shape, the metrics and span, the queue's cancel path, and the container wiring (Shigola mode never resolves a map provider or tile storage).
• Typecheck and lint pass against the new schema build.
• helm template renders with the token from the chart's Secret, from an existing Secret, and for the arcgis default.
• The integration suite was not run locally.

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