Ensure `@metadata()` content does not conflict with Bicep features persisted in metadata

**Is your feature request related to a problem? Please describe.**
The resource-typed params and outputs feature relies on writing a `resourceType` property to the parameter or output metadata. If a property with the same key is specified via an `@metadata()` decorator, the value used in the decorator will take precedence, leading to behavioral differences when consuming the template as compiled JSON/from a registry vs as a local .bicep file.

**Describe the solution you'd like**
A diagnostic should be emitted when a `resourceType` property is used in the metadata applied to an output or parameter.

Start by tracing how resource-typed parameters and outputs persist the `resourceType` property and how `@metadata()` decorators are processed. Find the existing diagnostic and test entry points for metadata or parameter/output validation, then add coverage showing that a `resourceType` key in applied metadata produces a diagnostic.

Written by the indexing model from the issue text.