Add EntityGraphHint query method parameter

[yeomin4242]

Repository query methods can now accept EntityGraphHint to select an entity graph per invocation.

The hint can be created from type-safe property paths, named entity graphs, or a JPA EntityGraph instance. We treat the hint as a special parameter so it is excluded from query binding and apply it for runtime and AOT query creation. If the argument is null, query creation falls back to the declared @EntityGraph metadata.

Includes unit and integration tests for parameter discovery, runtime query creation, repository execution, and AOT query generation.

Closes #4175

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