Tasks: slim-payment-providers

1. Remove concrete provider modules

1.1 Delete packages/universal/payment-providers/src/providers/stripe/.
1.2 Delete packages/universal/payment-providers/src/providers/paypal/.
1.3 Delete packages/universal/payment-providers/src/providers/square/.
1.4 Delete packages/universal/payment-providers/src/providers/mollie/.
1.5 Delete packages/universal/payment-providers/src/providers/adyen/.
1.6 Delete the now-empty src/providers/ directory.
1.7 Drop the SquareConfig type from src/types/provider.ts (it ships with the sibling Square package).
1.8 Remove the 5 ./providers/<name>/<name> entries from package.json#exports.

2.1 Promote the internal composeSignals function in src/http/http.ts to an exported composeAbortSignal(internal, external).
2.2 Re-export composeAbortSignal from src/http/index.ts and src/index.ts.
2.3 Extend src/http/http.test.ts to cover composeAbortSignal directly (internal abort propagates, external abort propagates, already-aborted external triggers immediately, undefined external returns internal).
2.4 Update src/http/http.md to document composeAbortSignal.

3.1 Extend the PAYMENT_PROVIDER_CODES registry in src/error-codes/error-codes.ts with PROVIDER_NOT_REGISTERED and PROVIDER_ALREADY_REGISTERED.
3.2 Add providerNotRegistered(name) and providerAlreadyRegistered(name) factories.
3.3 Extend src/error-codes/error-codes.test.ts to confirm both new codes are reachable from their factories and carry the provider discriminant when the registry surfaces them.
3.4 Update src/error-codes/error-codes.md to list all 6 codes.

4.1 Create src/registry/registry.ts exporting a ProviderRegistry class with register, unregister, get, has, list, size.
4.2 get(name) MUST throw PaymentProviderError(PROVIDER_NOT_REGISTERED) on miss.
4.3 register(provider) MUST throw PaymentProviderError(PROVIDER_ALREADY_REGISTERED) when the name is already present.
4.4 list() MUST return a frozen array in insertion order.
4.5 Create src/registry/registry.md with the §4 mandatory sections (Purpose, Features, Basic + Advanced usage, API Reference, Implementation Notes).
4.6 Create src/registry/registry.test.ts covering every public method, both error paths, and the insertion-order guarantee.

5.1 Create src/registry/define.ts exporting definePaymentProvider<TName extends string>(spec).
5.2 Result MUST be frozen and MUST carry the literal TName.
5.3 Method identities MUST be preserved (the closure passed in IS the closure dispatched at call time).
5.4 Create src/registry/define.md with the §4 mandatory sections.
5.5 Create src/registry/define.test.ts covering the literal-type narrowing, frozen-shape guarantee, method-identity preservation, and the round-trip through ProviderRegistry.register.

6.1 Create src/registry/index.ts re-exporting ProviderRegistry and definePaymentProvider via explicit named exports (rule 6a).
6.2 Rewrite src/index.ts to drop the 5 provider class exports and the SquareConfig type export, and add ProviderRegistry, definePaymentProvider, composeAbortSignal, providerNotRegistered, providerAlreadyRegistered.
6.3 Add ./registry/registry to package.json#exports. Final count: 5 entries (., ./types/provider, ./error-codes/error-codes, ./http/http, ./registry/registry).
6.4 Update package.json#description to describe the slim core.

7.1 Rewrite the one-paragraph description to reflect the slim shape.
7.2 Rewrite the Quick Start example to use ProviderRegistry + a sibling-imported StripeProvider.
7.3 Rewrite the Features list to drop the 5-adapter language and describe the foundation surface.
7.4 Rewrite the Modules list — only types/provider, error-codes/error-codes, http/http, registry/registry.
7.5 Add a "Sibling provider packages" section linking the 5 follow-up packages by name (note they are not yet published).

8.1 Step 0 — spec reconciliation: walk every ### Requirement in the delta, grep src/ for the named symbols, confirm every **Verified by:** test name appears in the matching test file.
8.2 Step 1 — bunx turbo lint typecheck test --filter=@suaveplan/payment-providers.
8.3 Step 2 — bunx turbo test:coverage --filter=@suaveplan/payment-providers reports 100/100/100/100.
8.4 Step 3 — bunx turbo build --filter=@suaveplan/payment-providers.
8.5 Step 4 — banned-pattern scan returns zero output.
8.6 Step 4a — barrel-shape scan returns zero output (no export * in any <feature>/index.ts).
8.7 Step 4b — test-runner import scan returns zero output (no direct vitest / bun:test imports).
8.8 Step 5 — every .ts (excl. .test.ts, .types.ts, index.ts) has a sibling .md.
8.9 Step 6 — README.md exists.
8.10 Step 7 — no bare versions in package.json.
8.11 Step 8 — subpath-export count matches the feature-module count (4 features + root = 5 entries).
8.12 Step 9 — security scan returns zero output.
8.13 Step 10 — dependent sweep: bunx turbo test --filter=...@suaveplan/payment-providers green (currently only the package itself).

9.1 Run bun scripts/folder-reorg/generate-manifest.ts to refresh MANIFEST.md.
9.2 Run bun scripts/generate-missing.ts to refresh MISSING.yml.
9.3 Hand-edit STATUS.md row for @suaveplan/payment-providers to describe the slim shape (no row flip — package stays ✅).
9.4 Hand-edit SUMMARY.md paragraph for @suaveplan/payment-providers to describe the slim shape.
9.5 bunx markdownlint-cli2 --fix across touched docs.

10.1 Fold specs/payment-providers/spec.md into openspec/specs/payment-providers/spec.md — apply the ## REMOVED block (delete the 5 provider requirements + drop SquareConfig from the http/types requirement) and apply the ## ADDED block (add the ProviderRegistry, definePaymentProvider, composeAbortSignal, and registry-code requirements).
10.2 Move openspec/changes/slim-payment-providers/ → openspec/archive/2026-05-17-slim-payment-providers/.