Revert name fields from agent configs, add getAgentConfigKey reverse lookup

Remove crash-causing name fields from 6 agent configs (sisyphus, hephaestus,
atlas, metis, momus, prometheus). The name field approach breaks opencode
because Agent.get(agent.name) uses name as lookup key.

Add getAgentConfigKey() to agent-display-names.ts for resolving display names
back to lowercase config keys (e.g. 'Atlas (Plan Executor)' -> 'atlas').

src/agents/metis.ts

@@ -311,7 +311,6 @@ 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,