Self-hosted endpoints on a LAN are sometimes protected by an API key. The admin
"Local" add/test form only sent base_url (+ model_type), so such an endpoint
could not be added — it just errored out — even though the backend
POST /api/model-endpoints and /model-endpoints/test already accept an optional
api_key form field (the cloud "API" form already uses it).
Adds an optional masked "API key" input (adm-epLocalApiKey) to the Local form
and wires it into the local Test and Add handlers, sending api_key only when
filled (an empty value is omitted so we never send a blank Bearer). The field
is cleared after a successful add, matching the cloud form.
Tested: tests/test_local_endpoint_api_key_js.py extracts the two click handlers
and runs them under node with mocked DOM/FormData/fetch, asserting api_key is
sent when the field is filled and omitted when blank, plus that the input
exists as a password field. `node --check static/js/admin.js` passes.
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>