feat(web): re-land the goals wire domain as mutation-only ref acknowledgements

Six mutation RPCs (create/edit/pause/resume/complete/clear) move into
dsh-host-apiproxy (the PR's host/runtime carrier is gone): goalService()
resolves ctx.get('goals') with a loud absence error, mutateGoal() resolves
the session's agent (agentFor, the command.* implicit-resume precedent) and
acknowledges with the new CAS ref only. GoalError codes ride err.details.

goal.get and the wire GoalView/goalViewSchema are gone: the read side is the
'goal' session projection (whole values on the history tail page and
session/projection frames), so responses never feed client state — the rule
whose absence forced the original PR's write-revision fences.

packages/host/apiproxy/tests/fetch-carrier.spec.ts

@@ -136,9 +136,6 @@ function fakeApi(overrides: Partial<{ muxFrames: MuxFrame[]; hostFrames: HostFra
       },
     },
     goals: {
-      async get(request) {
-        return { rpcId: request.rpcId, result: { ok: false, error: { code: 'internal', message: 'stub', details: {} } } }
-      },
       async create(request) {
         return { rpcId: request.rpcId, result: { ok: false, error: { code: 'internal', message: 'stub', details: {} } } }
       },