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/metis.ts

@@ -311,6 +311,7 @@ const metisRestrictions = createAgentToolRestrictions([
 
 export function createMetisAgent(model: string): AgentConfig {
   return {
+    name: "Metis (Plan Consultant)",
     description:
       "Pre-planning consultant that analyzes requests to identify hidden intentions, ambiguities, and AI failure points. (Metis - OhMyOpenCode)",
     mode: MODE,