Store a memory for an agent/user pair. Content is embedded locally (ONNX)
and persisted to Postgres. Returns the memory ID on success.

Args:
    agent_id:     Unique identifier for the agent storing the memory.
    user_id:      Unique identifier for the user this memory belongs to.
    content:      The text to remember (max 8000 chars).
    memory_type:  'episodic' (events/conversations), 'semantic' (facts/preferences),
                  or 'procedural' (workflows). Default: episodic.
    importance:   Weight multiplier 0.0–2.0. Use >1.0 for critical facts. Default: 1.0.

Search memories using semantic similarity + recency decay. Returns top-k
ranked results with scores.

Args:
    agent_id:     Agent whose memories to search.
    user_id:      User whose memories to search.
    query:        Natural language description of what to recall.
    top_k:        Number of memories to return (1–50). Default: 5.
    alpha:        Blend weight 0.0–1.0. 1.0 = pure semantic, 0.0 = pure recency.
                  Default: 0.7.
    memory_type:  Filter to 'episodic', 'semantic', or 'procedural'. Omit to search all.

Delete a specific memory by ID. The agent_id is used as an ownership check —
agents cannot delete each other's memories.

Args:
    agent_id:   Agent that owns the memory.
    memory_id:  UUID of the memory to delete (from store_memory or search_memories).

Return the total number of stored memories for an agent/user pair.

Args:
    agent_id:  Agent identifier.
    user_id:   User identifier.