fix(acpx): require the complete runtime contract behind the lazy prox…

fix(acpx): require the complete runtime contract behind the lazy proxy (#124628)

The ACPX lazy runtime proxy optional-chained every forwarded hook and
fabricated success when the resolved runtime lacked one: doctor() returned
{ ok: true }, getStatus() returned {}, and setMode/setConfigOption/
prepareFreshSession silently no-opped. Combined with the session-reset
service calling prepareFreshSession through two raw optional chains, an
unregistered or incomplete backend made reset preparation a silent no-op:
the reset appeared to succeed while the backend kept resuming the old
conversation.

Contract decision: the SDK-level AcpRuntime type keeps optional hooks
(third-party backends legitimately omit capabilities, and core consumers
gate on presence), but every runtime the ACPX extension resolves
implements the full surface. A new CompleteAcpRuntime type in the
extension makes those hooks required for proxy-resolved runtimes, so an
absent hook is a compile error instead of a fabricated runtime success.
The now-dead legacy runTurn->startTurn adapter (~190 LOC) is deleted with
its tests; the proxy forwards startTurn directly.

The session-reset-service call sites consolidate onto the control-plane
owner helper tryPrepareFreshManagerRuntimeSession, which now records a
visible outcome for every skipped path (backend not registered, hook not
supported) instead of returning silently; that also covers the same
silent skip in manager.close-session.

Regression tests fail pre-fix: proxy hooks reject on contract-violating
runtimes instead of fabricating success, and skipped fresh-session
preparation is recorded.