Dashboard search returns server error for an unknown resource type #8143

Feature Summary

The dashboard search dispatch throws an unhandled IllegalArgumentException for an unknown resourceType, so the API reports an internal server error for invalid client input.

Before: unknown resource type returns 500.
After: unknown resource type returns 400 with a specific message.

Reproduction evidence:

1. Start the local development backend from main.
2. Request GET /api/dashboard/publicSearch?resourceType=bogus.
3. Observe HTTP 500.
4. Request the same endpoint with resourceType=workflow and observe HTTP 200.

Version and commit evidence:

1.3.0-incubating-SNAPSHOT (main)

Commit Hash (Optional)

98588bf

What browsers are you seeing the problem on?

Not browser-specific.

Relevant log output

The request is logged as an unhandled IllegalArgumentException with Unknown resource type: bogus.

Proposed Solution or Design

After: unknown resource type returns 400 with a specific message.

Affected Area

Workflow Engine (Amber)