fix: address review feedback on auth inputs and dead base-action options

- Drop anthropic_api_key from repo workflows: only CLAUDE_CODE_OAUTH_TOKEN
  is configured as a secret, and upstream docs say to pick one auth path
- Replace the undeclared allowed_tools input in test workflows with
  claude_args --allowedTools (base-action only declares claude_args)
- Remove dead ClaudeOptions fields and INPUT_* reads that prepareRunConfig
  never consumed (mcp_config, allowed_tools, max_turns, system prompts, etc.)
- Update base-action README to document the actual inputs, with former
  dedicated inputs expressed as Claude CLI flags via claude_args

.github/workflows/issue-triage.yml

@@ -22,7 +22,6 @@ jobs:
         uses: anthropics/claude-code-action@main
         with:
           prompt: "/label-issue REPO: ${{ github.repository }} ISSUE_NUMBER${{ github.event.issue.number }}"
-          anthropic_api_key: ${{ secrets.ANTHROPIC_API_KEY }}
           claude_code_oauth_token: ${{ secrets.CLAUDE_CODE_OAUTH_TOKEN }}
           allowed_non_write_users: "*" # Required for issue triage workflow, if users without repo write access create issues
           github_token: ${{ secrets.GITHUB_TOKEN }}