Fix/graph recall rebind 281

[sshekhar563]

Description

This PR resolves Issue #281 where graph-augmented recall silently degraded after a Soul was restored from its state.

The Bug

During initialization (MemoryManager.__init__), the RecallEngine was instantiated with a reference to an empty KnowledgeGraph.
When MemoryManager.from_dict() restored a state, it completely rebuilt the graph and rebounded manager._graph, but the manager._recall_engine continued holding onto the old, empty graph. Because of this stale reference, graph-augmented recall returned empty results for restored souls, even while new observations mutated the new graph correctly.

The Fix

• Rewired the graph reference inside from_dict() immediately after the KnowledgeGraph is restored: manager._recall_engine._graph = manager._graph.
• Confirmed that this is the lowest-risk approach for deserialization (other built-in stores like episodic/semantic are updated in-place via .model_validate so they do not suffer from this rebinding hazard).

Testing Added

• Added a regression test test_from_dict_rewires_recall_engine_graph to tests/test_memory/test_memory.py.
• The test explicitly mutates a graph, serializes it, and asserts that restored._recall_engine._graph is restored._graph after calling from_dict.

Fixes #281