AGE entity-projection alias audit

Environment: Apache AGE `1.8.0`, PostgreSQL `18.1`, image

## Reproduction

```cypher
CREATE (n {id: 1})
WITH n AS alias0
MATCH (alias0)
RETURN alias0
```

Observed error:

```text
ERROR: variable 'alias0' already exists
```

The same error occurs after a second boundary:

```cypher
CREATE (n {id: 1})
WITH n AS alias0
WITH alias0
MATCH (alias0)
RETURN alias0
```

The two renamed-alias queries both produced the existing-variable error. The
control query below succeeded and returned the created vertex:

```cypher
CREATE (n {id: 4})
WITH n
MATCH (n)
RETURN n
```

Therefore this is not a generic prohibition on reusing an already-bound
pattern variable. The failure is specific to the entity projection alias.

Start by running the two renamed-alias reproductions and the successful control query on Apache AGE 1.8.0 with PostgreSQL 18.1. Trace the entity projection alias handling and locate the relevant regression-test entry point. Done means both renamed-alias queries succeed without the existing-variable error while the control query remains successful.

Written by the indexing model from the issue text.