Public workflow retrieval returns 500 when unavailable

[carloea2]

Feature Summary

The public-workflow endpoint dereferences the database result without checking whether a public workflow was found. Missing workflows and existing private workflows therefore return 500 instead of 404.

Before: unavailable public workflow lookup returns 500.

Expected: unavailable public workflow lookup returns 404, while a public workflow still returns 200.

Reproduction evidence:

1. Launch Texera from current main.
2. Request GET /api/workflow/publicised/999999 and observe a 500 response.
3. Request the same path for an existing private workflow and observe another 500 response.
4. Request it for a public workflow and observe a 200 response.

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 endpoint calls workflow getters after the public-only query returns no record.

Proposed Solution or Design

Expected: unavailable public workflow lookup returns 404, while a public workflow still returns 200.

Affected Area

Workflow Engine (Amber)

[carloea2]

/take