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/plugin-handlers/prometheus-agent-config-builder.ts

@@ -66,7 +66,7 @@ export async function buildPrometheusAgentConfig(params: {
     params.pluginPrometheusOverride?.maxTokens ?? categoryConfig?.maxTokens;
 
   const base: Record<string, unknown> = {
-    name: "prometheus",
+    name: "Prometheus (Plan Builder)",
     ...(resolvedModel ? { model: resolvedModel } : {}),
     ...(variantToUse ? { variant: variantToUse } : {}),
     mode: "all",