Add Schematic environment catalog integration

[snowmead]

Summary

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

Test plan

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

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Note

Low Risk
Additive catalog provider registration with tests only; no changes to auth, existing providers, or runtime provisioning paths beyond the new registry row.

Overview
Adds Schematic as a managed Stripe Projects integration for schematic/schematic-environment, so stacks can declare a Schematic integration and reference ${integrations.<name>.api_key} in service env.

The new SchematicEnvironment resource is wired into the provider registry and module tree like other Wave catalog providers: global-only config with optional environment_type and name, resource kind integration-schematic, and provisional api_key output mapping until mise run discover pins the envelope. validate_config is a no-op for now; catalog alignment and hermetic provision behavior are covered by unit tests (including catalog_outputs_match_output_fields).

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