fix: resolve --agent override via config alias before raw command

When --agent is passed to uwf thread exec, try config.agents[alias]
first (e.g. 'hermes' → config.agents.hermes = {command: 'uwf-hermes'}),
then fall back to parseAgentOverride for raw command names.

Also change eval CLI default --agent from 'hermes' to 'uwf-hermes'
so it works without config alias lookup.

Refs #91

packages/eval/src/commands/run.ts

@@ -52,7 +52,7 @@ export function registerRunCommand(program: Command): void {
   program
     .command("run <task>")
     .description("Run eval on a task directory or tarball")
-    .option("--agent <name>", "agent adapter to use", "hermes")
+    .option("--agent <name>", "agent adapter to use", "uwf-hermes")
     .option("--model <model>", "model override")
     .option("--count <n>", "number of eval runs", "1")
     .action(async (task: string, opts: RunCliOptions) => {