fix: Refine flow — optimistic UI update + instruction passthrough

- Add getActiveRefineAgent to spawn mutation optimistic updates and
  live event invalidation rules so the refine panel reflects agent
  state immediately without manual refresh
- Accept optional instruction param in buildRefinePrompt() and inject
  it as <user_instruction> block so the agent knows what to focus on
- Pass input.instruction through in architect router spawn call

apps/server/trpc/routers/architect.ts

@@ -265,7 +265,7 @@ export function architectProcedures(publicProcedure: ProcedureBuilder) {
           status: 'in_progress',
         });
 
-        const prompt = buildRefinePrompt();
+        const prompt = buildRefinePrompt(input.instruction);
 
         return agentManager.spawn({
           name: input.name,