feat(integrations): add privy Stripe catalog provider

[snowmead]

Summary

• Adds the privy 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

Medium Risk
New auth integration exposes app_secret via provisioning outputs; provisional output envelopes could mismatch live Stripe until discover is run.

Overview
Adds Privy as a Phase 1 Stripe Projects catalog integration: privy/app is wired as managed CatalogResource PrivyApp (provider = "privy", required app_name, outputs app_id / app_secret), registered in register_providers! with catalog gap and hermetic provision tests. OUTPUT_FIELDS stay provisional until mise run discover privy/app.

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

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