feat(ui): enable partial matching for collection search

[stevefulme1]

Summary

• Adds a "Collection name" filter using name__icontains for partial name matching — typing "sap" now returns all SAP-related collections (e.g., community.sap, community.sap_operations, etc.)
• Changes the Namespace filter from exact match (namespace=X) to partial match (namespace__icontains=X) — typing "cisco" returns all Cisco namespaces
• Keywords filter is unchanged — it continues to use the backend's full-text search across name, namespace, description, and tags

Problem

Previously, the Name and Namespace filters required exact matches. A user searching for "sap" in the name field would only find a collection named exactly "sap", missing collections like sap_hana, sap_operations, etc. This made content discovery unnecessarily difficult.

How it works

The Pulp/Django backend supports Django-style field lookups. The frontend now sends:

• name__icontains=sap instead of requiring exact name match
• namespace__icontains=cisco instead of namespace=cisco

These are case-insensitive substring matches handled natively by the backend.

Ref: AAP-67482

Test plan

• Search by "Collection name" filter with partial text (e.g., "sap") — verify partial matches returned
• Search by "Namespace" filter with partial text (e.g., "cisco") — verify partial matches returned
• Verify "Keywords" search still works for broad full-text search
• Verify empty state correctly shows when no filters are set
• Verify TypeScript compiles without errors (npm run lint:ts)

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