fix(tui): tighten cold-start edge cases after review

Clean up the remaining review nits:

- let the deferred @hermes/ink import retry after a transient failure instead
  of memoizing a rejected promise forever
- keep memory-monitor in-flight state inside a finally so future exceptions
  cannot suppress that memory level indefinitely
- use read_raw_config for the TUI MCP cold-start probe instead of full
  load_config()
- keep input.detect_drop for explicit relative path prefixes (./ and ../)
  while preserving the no-RPC fast path for ordinary plain prompts

Tests:
- python -m py_compile tui_gateway/server.py tui_gateway/entry.py
- cd ui-tui && npm run type-check && npm run build
- scripts/run_tests.sh tests/tui_gateway/test_protocol.py::test_sess_found tests/tools/test_code_execution_modes.py tests/tools/test_code_execution.py
- cd ui-tui && npm test -- --run src/__tests__/useSessionLifecycle.test.ts src/__tests__/useConfigSync.test.ts

tui_gateway/entry.py

@@ -175,8 +175,8 @@ def main():
     # loaded once by ``_config_mtime`` elsewhere) and only pay the import
     # cost when there's actually MCP work to do.
     try:
-        from hermes_cli.config import load_config
-        _mcp_servers = (load_config() or {}).get("mcp_servers")
+        from hermes_cli.config import read_raw_config
+        _mcp_servers = (read_raw_config() or {}).get("mcp_servers")
         _has_mcp_servers = isinstance(_mcp_servers, dict) and len(_mcp_servers) > 0
     except Exception:
         # Be conservative: if we can't decide, fall back to the old