feat(integrations): add metronome Stripe catalog provider

[snowmead]

Summary

• Adds the metronome Stripe Projects catalog integration family as CatalogResource adapter(s).
• Follows docs/ADDING-A-PROVIDER.md and docs/PROVIDER-WAVES.md.
• Includes gap test + hermetic provision test. OUTPUT_FIELDS provisional until mise run discover.

Test plan

• Gap + hermetic tests in module
• Live mise run discover when provider is linked
• Merge after resolving additive registry.rs conflict with other family PRs

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Note

Low Risk
Additive integration registration and SDK helpers with offline gap and hermetic tests; provisional output mapping is the main follow-up before live smoke.

Overview
Adds the Metronome Stripe Projects catalog family with a metronome/sandbox CatalogResource (provider = "metronome", ${integrations.*.api_key}), wired through register_providers!, providers/mod.rs, and an assert_outputs_match test. OUTPUT_FIELDS for API_KEY are provisional until mise run discover.

Extends stackless-provider-sdk with int_optional, bool_required, and bool_optional config readers for schema-driven integrations.

Documents catalog-first Phase 1 rollout in DECISIONS.md, PROVIDER-WAVES.md, and a link from ADDING-A-PROVIDER.md. Adds scripts/generate_catalog_integrations.py to scaffold remaining deployables from catalog.json.

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