fix(coder): include model in WS snapshot SELECT so the attribution chip survives refresh

CoderPane hydrates from the HTTP listMessages fetch (SELECT has model) AND the WS snapshot frame, and the snapshot handler setMessages-overwrites the HTTP load. The snapshot query in apps/coder/src/routes/ws.ts had its own column list that omitted model, so on coder refresh the chip's model was lost (it showed live via the message_complete frame). One-column fix: add model to that SELECT. CLAUDE.md mapper-chain note updated to list the WS snapshot SELECT.

apps/coder/src/routes/ws.ts

@@ -25,7 +25,7 @@ export function registerWebSocket(
 
       // Send snapshot of existing messages so client can hydrate
       const messages = await sql<Record<string, unknown>[]>`
-        SELECT id, session_id, chat_id, role, content, kind, tool_calls, tool_results, reasoning_parts, status, last_seq,
+        SELECT id, session_id, chat_id, role, content, kind, tool_calls, tool_results, reasoning_parts, status, model, last_seq,
                tokens_used, ctx_used, ctx_max, started_at, finished_at, created_at, metadata,
                summary, tail_start_id, compacted_at
         FROM messages_with_parts