fix(api): remove unused Harness status and ADK fields - #3454

…dev#3455)

Stacked on kagent-dev#3454.

Remove all Buf breaking-change exemptions, including excluded files and
unstable packages, so `FILE` compatibility applies after the final
pre-RC cleanup.

The CI check was silently skipping compatibility validation because the
checkout had no local `main` branch. Compare against the actual PR or
merge-group base SHA, or the previous commit on push, and fail when the
baseline is missing.

Validated protobuf lint, compatibility against the parent PR, and
workflow lint. Confirmed that the pre-cleanup API removals and a missing
baseline both fail instead of passing silently.

---------

Signed-off-by: Eitan Yarmush <[email protected]>

…on a status change (kagent-dev#3340)

## Problem
The ModelConfig status writer moves a condition's `lastTransitionTime`
whenever its reason, message or observedGeneration changes. Agent
conditions, and SandboxTemplate through `apimeta.SetStatusCondition`,
move it only when the status changes, as the API conventions define it.
A ModelConfig that stays `False` therefore reports a new transition time
every time its error text or generation changes.

## Change
Agent and ModelConfig share one helper that keeps the transition time
while a condition's status holds. A new test covers a changed reason,
message and generation under an unchanged status, and a status change.

This PR previously wrote Harness `Ready`/`Booted` conditions; kagent-dev#3454
removed `Harness.status`, so it is reduced to the transition-time rule
that part shared with Agent and ModelConfig.

Signed-off-by: QuentinBisson <[email protected]>