feat(integrations): add planetscale Stripe catalog provider

[snowmead]

Summary

• Adds the planetscale 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
Introduces paid database provisioning with credential database_url outputs that are provisional until discover; wrong output envelopes would break env interpolation at runtime, though the change follows the existing CatalogResource pattern with gap and hermetic tests.

Overview
Adds PlanetScale as a Phase 1 Stripe Projects catalog family with managed integrations for planetscale/mysql and planetscale/postgresql, wired through register_providers! and output-drift tests like other Cloudflare-style resources.

Each adapter is a standard CatalogResource: catalog-backed config (cluster, name, region; optional replicas on PostgreSQL), provisional database_url output mapping until mise run discover, plus offline gap tests and hermetic provision tests.

stackless-provider-sdk gains shared int_optional, bool_required, and bool_optional config helpers for generated and hand-written catalog modules. Documentation adds PROVIDER-WAVES.md, a catalog-first decision in DECISIONS.md, and a link from ADDING-A-PROVIDER.md; scripts/generate_catalog_integrations.py scaffolds future catalog families from the committed catalog fixture.

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