feat(integrations): add inngest Stripe catalog provider

[snowmead]

Summary

• Adds the inngest 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

---

Note

Low Risk
Additive integration and docs; provisioning follows the same shared Stripe catalog path as existing providers, with no auth or core lifecycle changes.

Overview
Adds the Inngest Phase 1 Stripe Projects integration for inngest/app: managed CatalogResource with required id, outputs event_key and signing_key (provisional OUTPUT_FIELDS until mise run discover), plus catalog gap and hermetic provision tests. Registers InngestApp in register_providers! and extends the output-drift test.

Also extends stackless-provider-sdk with optional/required boolean and integer config helpers for upcoming generated catalog adapters, documents catalog-first waves and exclusions in DECISIONS.md / new PROVIDER-WAVES.md, links that from ADDING-A-PROVIDER.md, and adds scripts/generate_catalog_integrations.py to scaffold remaining deployables (Inngest is the hand-landed family in this PR).

^{Reviewed by Cursor Bugbot for commit bf56fc3. Bugbot is set up for automated code reviews on this repo. Configure here.}