Add Depot API catalog integration

[snowmead]

Summary

• Phase 1 CatalogResource for depot/api (Wave 7).
• Registry row + providers/depot module, gap + hermetic provision tests.
• Provisional OUTPUT_FIELDS (api_key) until mise run discover depot/api.
• Branched from refresh tip 30df3de (plugin v0.25.0 fixtures). No smoke fixture.

Test plan

• cargo nextest run -p stackless-integrations -E 'test(depot)'
• registry uniqueness + catalog_outputs_match_output_fields
• mise run check (pre-push hook)

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Note

Low Risk
Additive provider registration and tests only; no changes to auth, provisioning core, or existing integrations.

Overview
Adds Depot as a managed Stripe Projects integration for the depot/api service (Wave 7 phase-1 CatalogResource).

New providers/depot defines DepotApi with global-only config, resource kind integration-depot, and a provisional api_key output mapped from DEPOT_API_KEY until discover pins the envelope. Wiring includes a registry row and provider module registration, plus catalog_outputs_match_output_fields coverage for DepotApi.

Tests verify catalog schema alignment against the shared fixture and hermetic provision that records api_key in the resource payload.

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