code: clarify Create-time status exception in store.go [ddx-e8956709]

Updated store.go:544-549 comment to explicitly document that Create-time
StatusOpen assignment is the sole exception to ValidateLifecycleTransition,
aligning with reconcile.go:239-243 which already documents the ClosureGate
bypass via TD-031 §3.1. All other Status writes flow through
transitionLifecycleInPlace + ValidateLifecycleTransition per TD-031.

Verified via grep that only two Status assignments exist:
- Create (line 549) with documented exception
- transitionLifecycleInPlace (line 762) which validates transitions

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

Author: ddx-checkpoint

cli/internal/bead/store.go

@@ -542,10 +542,10 @@ func (s *Store) Create(args ...any) error {
 		b.IssueType = DefaultType
 	}
 	if b.Status == "" {
-		// Bead creation is initial state assignment, not a lifecycle transition.
-		// This is the sole exception to transitionLifecycleInPlace: all other status
-		// writes go through transitionLifecycleInPlace + ValidateLifecycleTransition
-		// (TD-031 §3 transition matrix, transitionLifecycleInPlace pattern).
+		// Create-time StatusOpen assignment is initial state, not a lifecycle transition.
+		// This is the sole exception to ValidateLifecycleTransition: all other status
+		// writes go through transitionLifecycleInPlace, which validates transitions via
+		// ValidateLifecycleTransition (TD-031 §3 transition matrix pattern).
 		b.Status = DefaultStatus
 	}
 	b.CreatedAt = now