Fix auth token error code

[simonfaltum]

Changes

Use the standard UNAUTHENTICATED Databricks error code when databricks auth token --output json can't refresh a cached U2M token.

Example:

{
  "error_code": "UNAUTHENTICATED",
  "message": "A new access token could not be retrieved because the refresh token is invalid. To reauthenticate, run the following command:\n  $ databricks auth login --profile test-profile"
}

Why

#6684 introduced INVALID_REFRESH_TOKEN as an ad-hoc top-level error code. Databricks error code guidelines require using a standard code, and UNAUTHENTICATED is the closest match for cached credentials that are no longer valid. The existing error message and reauthentication guidance remain unchanged.

Tests

• go test ./cmd/auth ./libs/auth/...
• go test ./acceptance -run 'TestAccept/cmd/auth/token/force-refresh-invalid-refresh-token$' -tail -test.v
• ./task fmt
• ./task checks
• ./task lint
• ./task test (the auth changes pass; the unrelated bundle/templates/lakeflow-integrations test fails because its offline uv cache is missing charset-normalizer and certifi)

This PR was written by Codex.

[eng-dev-ecosystem-bot]

Integration test report

Commit: 19513c8

Run: 35321179545

	Env	✅​pass	🙈​skip	Time
✅​	aws linux	276	16	6:44
✅​	aws windows	278	14	5:23
✅​	azure linux	275	16	4:51
✅​	azure windows	277	14	5:18
✅​	gcp linux	276	16	6:00
✅​	gcp windows	278	14	6:37

Top 3 slowest tests (at least 2 minutes):

duration	env	testname
5:25	gcp windows	TestAccept
5:19	aws windows	TestAccept
5:15	azure windows	TestAccept