fix(mem0-agent): non-blocking stdin, clean session_state, lint

Found by running the CLI live against a scratch project:
- hook_input() blocked forever on an open stdin pipe with no data. A real hook
  writes JSON and closes the pipe, but any manual invocation hung; now polled
  with select() and never blocks.
- the open-thread snapshot was filling with progress lines and file-modification
  lists -- v1's exact failure -- so it now filters turns through the same
  hard-drop rules the capture gate uses.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

integrations/mem0-agent/src/mem0_agent/settings.py

@@ -231,7 +231,7 @@ class SessionState:
 
     def read_lines(self, name: str) -> list[dict]:
         try:
-            return [json.loads(l) for l in self._p(name).read_text().splitlines() if l.strip()]
+            return [json.loads(line) for line in self._p(name).read_text().splitlines() if line.strip()]
         except Exception:
             return []