Name filters use istartswith on most endpoints — substring search misses; inconsistent with activations/rulebooks

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- [x] I have checked the [current issues](https://github.com/ansible/eda-server/issues) for duplicates.
- [x] I understand that EDA-Controller is open source software provided for free and that I might not receive a timely response.

### Bug Summary

Six of the nine list endpoints used by the EDA role wizard filter `name` with `lookup_expr="istartswith"`, while three use `icontains`, so substring search silently misses on most endpoints — and the ansible-ui toolbar presents the filter as a "contains" search:

| Endpoint | `name` lookup |
|---|---|
| eda-credentials, projects, credential-types, decision-environments, event-streams | `istartswith` |
| activations, rulebooks, activation-instances | `icontains` |
| audit-rules | no `filterset_class` at all |

(See `src/aap_eda/api/filters/*.py`.)

Clients also cannot work around this with `?name__icontains=`: no FilterSet declares that lookup, and with no django-filter STRICTNESS configured the unknown param is silently ignored, returning the full unfiltered list.

### Environment

AAP 2.7 on OpenShift (eda-server-operator), EDA API version 1.3.2. Behavior is defined in the FilterSet declarations, so it is deployment-independent (same in standalone builds).

### Steps to reproduce

1. On an instance with the default credential types loaded, call `GET /api/eda/v1/credential-types/?name=auth`.
2. Call `GET /api/eda/v1/credential-types/?name__icontains=basic`.

### Actual results

1. `?name=auth` returns 0 results, even though "OAuth2 Event Stream" and "OAuth2 JWT Event Stream" exist (prefix-only match).
2. `?name__icontains=basic` returns all 28 credential types (param silently ignored, no filtering).

### Expected results

1. A name search presented as "contains" in the UI should match substrings: `?name=auth` should return the two OAuth2 types.
2. Ideally an unsupported filter param should not silently return the full unfiltered collection.

### Additional information

Suggested fix: change `lookup_expr` to `icontains` for the `istartswith` name filters (precedent already in-tree: `ActivationFilter`, `RulebookFilter`), and consider adding a `filterset_class` to `AuditRuleViewSet`. Backward-compatible: `icontains` matches are a strict superset of `istartswith` matches.

Refs: ansible/ansible-ui#3322 (where this was uncovered), ansible/django-ansible-base#1060 (related OPTIONS metadata regression found in the same investigation).

Start in src/aap_eda/api/filters/*.py and compare the name FilterSet declarations for the listed endpoints with ActivationFilter and RulebookFilter. Review the AuditRuleViewSet entry point, then verify the credential-types requests in the issue and confirm that substring searches consistently return matching results without changing unrelated filtering behavior.

Written by the indexing model from the issue text.