fix(mma-exec): strip ANTHROPIC_API_KEY from subprocess env to use subscription login

When ANTHROPIC_API_KEY is set in the shell environment, claude --print
routes through the API key instead of subscription auth. Stripping it
forces the CLI to use subscription login for all Tier 3/4 delegation.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

scripts/claude_mma_exec.py

@@ -197,6 +197,7 @@ def execute_agent(role: str, prompt: str, docs: list[str]) -> str:
  try:
   env = os.environ.copy()
   env['CLAUDE_CLI_HOOK_CONTEXT'] = 'mma_headless'
+  env.pop('ANTHROPIC_API_KEY', None)  # Force CLI to use subscription login, not API key
   process = subprocess.run(
    cmd,
    input=command_text,