fix: gracefully fall back to FileMemory when a string memory backend fails to initialise

CI test-core (subdirs) failed on test_every_advertised_preset_resolves with
"Mem0 API Key not provided" because the mem0 package is installed in that job
but no MEM0_API_KEY is set. Agent(memory="mem0") already promised a graceful
"Falling back to FileMemory" for missing optional dependencies (ImportError),
but an installed-yet-uninitialisable SaaS backend raised ValueError, which was
uncaught and crashed construction. Broaden the string-preset branch to honour
the same fallback contract for runtime init failures.

Pre-existing, unrelated to PR #4340 (gateway durability); no Agent params added.

Co-authored-by: Mervin Praison <[email protected]>

src/praisonai-agents/praisonaiagents/agent/agent.py

@@ -5781,6 +5781,14 @@ Summary:"""
                 logging.warning(f"Memory provider '{memory}' requires additional dependencies. Falling back to FileMemory.")
                 from ..memory.file_memory import FileMemory
                 self._memory_instance = FileMemory(user_id=mem_user_id)
+            except Exception as e:
+                # The backend package is installed but could not initialise
+                # (e.g. a SaaS backend like mem0 needs credentials/network).
+                # Honour the same "Falling back to FileMemory" contract used for
+                # missing dependencies so construction never hard-crashes.
+                logging.warning(f"Memory provider '{memory}' could not initialise ({e}). Falling back to FileMemory.")
+                from ..memory.file_memory import FileMemory
+                self._memory_instance = FileMemory(user_id=mem_user_id)
         elif isinstance(memory, dict):
             # Configuration dict
             provider = memory.get("provider", memory.get("backend", "file"))