Add display names to all core agents via name field

Sisyphus (Ultraworker), Hephaestus (Deep Agent), Prometheus (Plan Builder),
Atlas (Plan Executor), Metis (Plan Consultant), Momus (Plan Critic).

Requires opencode fix: Agent.get() fallback to name-based lookup when key
lookup fails, since opencode stores agent.name in messages and reuses it
for subsequent Agent.get() calls.

src/agents/sisyphus.ts

@@ -539,6 +539,7 @@ export function createSisyphusAgent(
     call_omo_agent: "deny",
   } as AgentConfig["permission"];
   const base = {
+    name: "Sisyphus (Ultraworker)",
     description:
       "Powerful AI orchestrator. Plans obsessively with todos, assesses search complexity before exploration, delegates strategically via category+skills combinations. Uses explore for internal code (parallel-friendly), librarian for external docs. (Sisyphus - OhMyOpenCode)",
     mode: MODE,