StandaloneAgentCard's resolveAgentCardModelLabel call had a top-level
provider field that the helper never reads — when input.agent is present,
it reads provider from input.agent.provider instead. Remove the dead field
and its three redundant copies in linked-agent regression tests.
Replace the inline template at AgentConfigFields:804 with a call to
formatDefaultModelLabel, which is already regression-tested for the
provider-scoped Databricks-name leak. Drop the now-unused resolveModelLabel
import. Derive fallbackModelLabel as a const to keep the JSX clean and
within the file-size ratchet.
Co-authored-by: Will Pfleger <pfleger.will@gmail.com>
Signed-off-by: Will Pfleger <pfleger.will@gmail.com>