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/atlas/agent.ts

@@ -99,7 +99,6 @@ export function createAtlasAgent(ctx: OrchestratorContext): AgentConfig {
   ])
 
   const baseConfig = {
-    name: "Atlas (Plan Executor)",
     description:
       "Orchestrates work via task() to complete ALL tasks in a todo list until fully done. (Atlas - OhMyOpenCode)",
     mode: MODE,