Task 3 ProviderCache interface evidence

Defined interface:

- `packages/model-core/src/provider-cache.ts`
  - `readConnectedProvidersCache(): string[] | null`
  - `findProviderModelMetadata(providerID: string, modelID: string): ModelMetadata | undefined`

Injection points:

- `packages/model-core/src/model-resolution-pipeline.ts`
  - `resolveModelPipeline(request, providerCache)` uses `providerCache.readConnectedProvidersCache()`.
- `packages/model-core/src/model-error-classifier.ts`
  - `selectFallbackProviderWithCache(providers, providerCache, preferredProviderID?)` uses `providerCache.readConnectedProvidersCache()`.

Adapter wiring in OMO:

- `src/shared/model-resolution-pipeline.ts` passes `connectedProvidersCache` into model-core resolver.
- `src/shared/model-error-classifier.ts` passes `connectedProvidersCache` into model-core provider selection.