v2: normalize or reject unprefixed AI SDK packages in native provider config

Problem

Native V2 provider configuration accepts an AI SDK npm package without the required aisdk: prefix, but the resulting provider fails only when a prompt is sent. This makes a plausible configuration silently select the native OpenCode provider loader instead of AI SDK compatibility.

{
  "providers": {
    "custom": {
      "package": "@ai-sdk/openai-compatible",
      "models": { "chat": {} }
    }
  }
}

The currently working form requires an undocumented/non-obvious discriminator:

{
  "providers": {
    "custom": {
      "package": "aisdk:@ai-sdk/openai-compatible",
      "models": { "chat": {} }
    }
  }
}

The same issue applies to model-level package overrides. Legacy V1 provider.*.npm and model-level provider.npm values are automatically normalized during migration, and models.dev packages are also normalized, so native V2 config behaves inconsistently with those sources.

Current implementation

• packages/core/src/config/plugin/provider.ts copies provider-level and model-level package values directly into the catalog.
• packages/core/src/provider.ts recognizes AI SDK packages only when prefixed with aisdk:.
• packages/core/src/model-resolver.ts treats every unprefixed package as a native OpenCode provider module.
• V2 provider and model config schemas currently accept the invalid-looking-but-runtime-broken bare AI SDK strings.

Expected behavior

Native V2 configuration should either normalize obvious AI SDK package names such as @ai-sdk/* at both provider and model levels, or reject them early with an actionable validation error explaining the required aisdk: prefix. The public V2 provider documentation should explain native versus AI SDK package selection.

Preserve legitimate unprefixed native provider modules and native file:// packages; arbitrary third-party AI SDK packages may still need an explicit discriminator.