feat(integrations): add wix Stripe catalog provider

[snowmead]

Summary

• Adds the wix 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 gap and hermetic tests; provisional output envelope is documented and unchanged from other providers until discover.

Overview
Adds the Wix Stripe Projects catalog family with a wix/headless CatalogResource (WixHeadless): optional plan and wix_project_name, managed/global-only hosting, and provisional app_id output until mise run discover. Registers (wix::headless, WixHeadless) and extends the catalog output-drift test for Wix.

Also extends stackless-provider-sdk with optional/required integer and boolean config helpers for generated catalog adapters, documents catalog-first waves and exclusions in PROVIDER-WAVES.md / DECISIONS.md, links waves from ADDING-A-PROVIDER.md, and adds scripts/generate_catalog_integrations.py to scaffold remaining deployables.

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