Test: embedding tests out of sync with current API behavior

[rajjaa-hr]

Summary

Two embedding tests in tests/test_text.py no longer match the current API behavior:

1. `test_embedding_basic` (tests/test_text.py:55)

Sends a text to `/text/embedding` without an `algorithm_key`. Expects 200, now gets:
```
400 Bad request. Algorithm key is required.
```
The backend now requires an algorithm key on this endpoint. The test needs to pass one (and a matching env var).

2. `test_embedding_no_text` (tests/test_text.py:66)

Asserts the 400 error message contains the substring `null`, but the API now returns:
```
Bad request. Texts cannot be empty
```
The assertion needs updating.

Suggested fix

• Add `HRFLOW_ALGORITHM_KEY_EMBEDDING` (or reuse an existing one) and pass it into `test_embedding_basic`.
• Update `test_embedding_no_text` to assert on a substring that matches the current message (e.g. `empty` or `cannot`), or ideally assert on a structured error code if the API exposes one.