feat(ultrawork): implement per-message model override with deferred DB retry strategy

- Add per-message ultrawork mode detection via keyword matching
- Implement deferred DB override strategy using microtask retry loop
- Fall back to setTimeout after 10 microtask retries for robustness
- Update agent configuration schema with ultrawork model/variant fields
- Integrate with chat.message hook to apply overrides on detection
- Add comprehensive tests for all override scenarios
- Generated schema includes ultrawork configuration

🤖 Generated with assistance of OhMyOpenCode (https://github.com/code-yeongyu/oh-my-opencode)

src/shared/model-requirements.test.ts

@@ -64,7 +64,7 @@ describe("AGENT_MODEL_REQUIREMENTS", () => {
     const explore = AGENT_MODEL_REQUIREMENTS["explore"]
 
     // when - accessing explore requirement
-    // then - fallbackChain exists with grok-code-fast-1 as first entry, minimax-m2.5-free as second
+    // then - fallbackChain: grok → minimax-free → haiku → nano
     expect(explore).toBeDefined()
     expect(explore.fallbackChain).toBeArray()
     expect(explore.fallbackChain).toHaveLength(4)