feat(integrations): add parallel Stripe catalog provider

[snowmead]

Summary

• Adds the parallel 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
Standard managed catalog adapter with offline tests; provisional output envelope is documented and matches existing Hyperdrive-style posture.

Overview
Adds the Parallel Stripe Projects catalog integration for parallel/api: managed CatalogResource with provider = "parallel", paid-pricing selectors (product defaulting to search, plus optional processor / generator / tier), and provisional api_key output until mise run discover. Registered in register_providers!, covered by catalog gap and hermetic provision tests, and included in the Hostable::OUTPUTS vs OUTPUT_FIELDS drift test.

Also extends stackless-provider-sdk with shared int_optional, bool_required, and bool_optional config helpers for upcoming generated adapters.

Documentation and tooling for parallel Phase 1 rollouts: PROVIDER-WAVES.md, a catalog-first decision in DECISIONS.md, a link from ADDING-A-PROVIDER.md, and scripts/generate_catalog_integrations.py (does not rewrite registry.rs / providers/mod.rs).

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