enumerateUsers wildcard append assumes string criteria values

Found during the 2.0.0 release-readiness review (see #144).

In `enumerateUsers` (`src/pas/plugins/ldap/plugin.py`, ~line 430):

```python
if not value.endswith("*"):
kw[key] = value + "*"
```

If a caller passes a non-string criterion value (e.g. an int), `value.endswith` raises `AttributeError`. In practice PAS passes strings, so the risk is low, but a `str()` coercion / `isinstance` guard would harden it.

Severity: low / hardening.

Start in src/pas/plugins/ldap/plugin.py around enumerateUsers and inspect how criterion values are handled before the wildcard is appended. Confirm the expected behavior for non-string values, add coverage for an integer criterion, and run the relevant test suite to verify that string criteria still receive the correct wildcard handling.

Written by the indexing model from the issue text.