Fixes #29726

Summary

• add an optional startup timeout for MCP discovery and let timed-out discovery continue on the MCP background loop
• use a short bounded wait during CLI and gateway startup so slow optional MCP servers do not block Hermes boot
• cover the soft-fail startup path with a targeted MCP discovery test

Testing

• uv run --frozen pytest -q -o addopts= tests/tools/test_mcp_tool.py -k 'startup_soft_fail or failed_count'\n- uv run --frozen ruff check tools/mcp_tool.py hermes_cli/main.py gateway/run.py tests/tools/test_mcp_tool.py\n- git diff --check