Align terminal-auth validation and docs with the current ACP RFD

[hetaoBackend]

The registry currently has two terminal-auth compatibility mismatches with the current ACP RFD:

1. .github/workflows/client.py advertises clientCapabilities.terminal: true plus _meta["terminal-auth"], but not the current v1 capability clientCapabilities.auth.terminal: true. A conforming agent that only checks the current capability returns no terminal auth method, so verify_agents.py --auth-check fails with No authMethods in response.
2. AUTHENTICATION.md says terminal-auth args replace the default launch args. The current RFD specifies that clients reconstruct the configured base launch and append the descriptor args. Zed already implements the append behavior.

Current RFD: https://agentclientprotocol.com/rfds/auth-methods
Validator:

registry/.github/workflows/client.py

Lines 214 to 233 in 921b987

	proc = None
	t0 = time.monotonic()
	try:
	# Make binary executable if needed
	exe_path = Path(cmd[0])
	if exe_path.exists() and not os.access(exe_path, os.X_OK):
	exe_path.chmod(exe_path.stat().st_mode | 0o755)
	# Start agent process
	proc = subprocess.Popen(
	cmd,
	cwd=cwd,
	env=full_env,
	stdin=subprocess.PIPE,
	stdout=subprocess.PIPE,
	stderr=subprocess.PIPE,
	text=True,
	bufsize=0,
	**subprocess_group_kwargs(),

Docs:

registry/AUTHENTICATION.md

Lines 65 to 78 in 921b987

	"type": "terminal",
	"args": ["--setup"],
	"env": {
	"VAR1": "value1"
	}
	}
	```
	**Key points:**
	- The `args` array specifies additional command-line arguments (e.g., `--setup`, `--login`)
	- The `env` object defines environment variables to pass to the process
	- These **replace** the default args/env for the agent during the setup flow
	- The agent should handle its interactive login flow separately from standard ACP operation

Suggested compatibility-safe change:

• Have the auth validator advertise auth: { terminal: true } while retaining the legacy hints during the preview transition.
• Update AUTHENTICATION.md to describe base launch + appended args and env overlay semantics.
• Add a validator test for an agent that gates terminal auth on clientCapabilities.auth.terminal.

I found this while preparing a registry entry for MiniMax Code; its current ACP implementation follows the RFD capability shape and reproduces the auth-check failure.

[hetaoBackend]

Contributor intent: I plan to submit a focused PR from hetaoBackend covering the validator capability shape, the documented append semantics, and a regression test. I will keep the MiniMax Code agent-entry contribution separate so this compatibility fix does not depend on that package release.