feat(fixture): mirror the goal domain — /goal command, six verbs, projection unit

The keyless fixture now carries the goal chain end to end, mirroring the
host: /goal enters the command catalog and its execute path brackets a
goal/change create with the command lifecycle pair; the six mutation verbs
CAS-check the projected current goal and append whole-value changes (the
shared append path broadcasts the session event and the goal projection
frame); the tail-page projections block and the mux-open baseline always
carry the goal key (null before create / after clear). Connection specs
follow: the lifecycle round-trip replaces the not-implemented stubs, and
the mux baseline expects the third unit frame.

Also: GoalBar inline errors use ASCII parens around the code (review
feedback on #842).

packages/client/ui-goal/src/client/GoalBar.tsx

@@ -52,7 +52,7 @@ export function GoalBar({ goal, onEdit, onResume, onClear }: GoalBarProps) {
     if (result.ok) {
       setEditing(false)
     } else {
-      setActionError(`${result.error.message}（${result.error.code}）`)
+      setActionError(`${result.error.message} (${result.error.code})`)
     }
   }, [draft, onEdit])
 
@@ -61,7 +61,7 @@ export function GoalBar({ goal, onEdit, onResume, onClear }: GoalBarProps) {
     setActionError(null)
     const result = await action()
     setPending(false)
-    if (!result.ok) setActionError(`${result.error.message}（${result.error.code}）`)
+    if (!result.ok) setActionError(`${result.error.message} (${result.error.code})`)
   }, [])
 
   // Loading, absent, and complete goals have no strip at all.