fix(buzz-acp): treat hermes-acp as a zero-arg agent

[mikeholownych]

Summary

• `default_agent_args()` already special-cases other zero-arg ACP adapters (`codex-acp`, `claude-agent-acp`, `buzz-agent`), and `default_agent_env()` a few lines above already special-cases `hermes`/`hermes-agent`/`hermes-acp` by name — but `default_agent_args()` was missing the same three identities.
• Without this, the harness's clap default (`"acp"`) is passed straight through as a positional argument to `hermes-acp`, which doesn't expect one.

Test plan

• Built `buzz-acp` in release mode and ran it against a local relay with `BUZZ_ACP_AGENT_COMMAND=hermes-acp`; confirmed it spawns `hermes acp` with no stray positional argument and authenticates successfully (NIP-42 auth succeeded, presence set to online).

[ScaleLeanChris]

Field-tested this against a real stock Hermes installation and an authorized private Buzz channel.

Evidence:

• Before this patch, the Hermes preset fails during ACP initialization with hermes: error: unrecognized arguments: acp.
• At 743eee74c, the same identity, relay, and channel start successfully with no appended acp argument.
• buzz-acp logs Starting hermes-agent ACP adapter, completes ACP v2 initialization, creates a session, receives the channel prompt, and Hermes completes the turn.
• Focused config suite: 113 passed, 0 failed.

I temporarily stopped the supervised Hermes gateway to avoid a duplicate consumer during the test and restored it afterward. This validates the narrow compatibility claim: the bundled hermes-acp launcher is a zero-argument ACP command.