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

ui-tui/src/app/useSubmission.ts

@@ -127,9 +127,9 @@ export function useSubmission(opts: UseSubmissionOptions) {
       }
 
       // Plain prompts are the common path and should not pay an extra RPC
-      // before prompt.submit. File-drop detection can still run for inputs
-      // that contain an absolute/tilde path or file:// URI.
-      if (!looksLikeSlashCommand(text) && !/(?:^|\s)(?:file:\/\/|~\/|\/)[^\s]+/.test(text)) {
+      // before prompt.submit. File-drop detection still runs for absolute,
+      // tilde, file://, and explicit relative paths.
+      if (!looksLikeSlashCommand(text) && !/(?:^|\s)(?:file:\/\/|~\/|\.?\.\/|\/)[^\s]+/.test(text)) {
         return startSubmit(text, expand(text), showUserMessage)
       }