Conversations and sessions now track whether they originated locally or remotely

What

• SessionController gained conversationOrigin and preClearOrigin state; resetting a conversation now records the prior origin and resets conversationOrigin back to "local".
• A new markConversationRemote callback was wired into the query-event context and threaded through the main session-loop context object.
• A Stop-hook path calls markConversationRemote to set the session's conversationOrigin to "remote".

Why This lets Claude Code distinguish conversations that originated remotely from local ones, which other logic (such as artifact-state reconstruction) can use to handle them differently.