chore: prune legacy config switches

[jackwener]

Summary

• remove OUTPUT env override and DEBUG=opencli fallback from runtime behavior
• stop exposing dead or internal-only config names in public docs and workflow examples
• drop stale OPENCLI_BROWSER_EXECUTABLE_PATH injections from CI workflows

Verification

• npm run typecheck
• npx vitest run src/output.test.ts --reporter=verbose
• manual logger checks for OPENCLI_VERBOSE vs DEBUG fallback removal

[jackwener]

LGTM. Reviewed the diff — all five ghost/obsolete configs are cleanly removed from runtime code, CI workflows, docs, and tests. Verified no remaining references to OPENCLI_BROWSER_EXECUTABLE_PATH, OPENCLI_DAEMON_TIMEOUT, or OPENCLI_HEADLESS in the codebase. Ready to merge.