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/agent/prompts/refine.ts

@@ -4,7 +4,10 @@
 
 import { CODEBASE_EXPLORATION, INPUT_FILES, SIGNAL_FORMAT } from './shared.js';
 
-export function buildRefinePrompt(): string {
+export function buildRefinePrompt(instruction?: string): string {
+  const instructionBlock = instruction
+    ? `\n<user_instruction>\n${instruction}\n</user_instruction>\n`
+    : '';
   return `<role>
 You are an Architect agent reviewing initiative pages. You do NOT write code.
 </role>
@@ -17,7 +20,7 @@ Write one file per modified page to \`.cw/output/pages/{pageId}.md\`:
 - Frontmatter: \`title\`, \`summary\` (what changed and why)
 - Body: Full replacement markdown content for the page
 </output_format>
-
+${instructionBlock}
 <improvement_priorities>
 1. **Ambiguity**: Requirements interpretable multiple ways → make specific
 2. **Missing details**: Gaps forcing agents to guess → fill with concrete decisions