Browser autofills hidden api_key override field on Flow Model, breaking provider authentication

**Title:** Browser autofills hidden `api_key` override field on Flow Model, breaking provider authentication

**Description:**
When a user configures an API key inside a `Flow Provider`, the `api_key` override field in the linked `Flow Model` DocType is typically hidden. However, because the hidden field is still rendered as a password input in the DOM, browser password managers aggressively autofill it with the user's saved Frappe site password (e.g., the `Administrator` login password).

Because Frappe serializes and saves hidden fields, simply clicking "Save" on the `Flow Model` document silently writes the autofilled login password into the database as the model's override key. Since `FlowModel.test_connection` and LiteLLM prioritize the model's override key over the global Provider key, the API call fails with an invalid credential error.

**Steps to Reproduce:**
1. Create a `Flow Provider` and save a valid API key.
2. Ensure your browser (or password manager) has a saved login password for your Frappe instance.
3. Open a `Flow Model` record linked to that Provider. The model's `api_key` field will be hidden.
4. Save the `Flow Model` document.
5. Click **Test Connection**. The request will fail because it is sending the site login password instead of the provider's API key.

**Expected Behavior:**
Hidden password fields should not capture autofilled credentials, preventing the user's login password from accidentally overriding the Provider's configuration.

**Suggested Fixes:**
1. Add `autocomplete="new-password"` to the `api_key` field's HTML attributes to deter aggressive browser autofill.
2. Alternatively, implement a standard Frappe client script (`on_save` hook) in `Flow Model` that explicitly clears the `api_key` field before saving if the field is currently hidden by its `depends_on` condition.

Start at the Flow Model DocType's hidden api_key field and its Test Connection flow; reproduce the issue with a saved Frappe password and inspect the field before saving. Done when saving a model does not persist the autofilled login password and Test Connection continues using the linked Provider key.

Written by the indexing model from the issue text.