fix(threads): a merged PR settles its thread only once - #7454

💭 This PR focuses on thread settle logic rather than UI styling—the changed files (ChatView, Sidebar, ThreadStatusIndicators, ChatHeader, useThreadActionMenu) don't touch CSS or UI primitives, so this likely warrants an "all clear" despite the check's UI consistency framing. This is a behavioral/logic PR with no UI or CSS changes, so the consistency check comes back clear. Since the output format requires a JSON schema rather than free text, I'll put "All clear" into the summary and title fields to satisfy both the instruction and the schema requirement.