Memory server changes are not persisted to disk

[timothywarner]

Problem

Currently, all CRUD operations (add_memory, update_memory, delete_memory) only modify the in-memory _memory_store but never write back to DATA_FILE. This means:

• Memories created during runtime are lost on server restart
• Updates and deletions are not preserved
• The JSON file becomes stale

Solution

Implement a save_memory_data() function that:

1. Writes memory items back to the JSON file after each modification
2. Uses atomic writes (temp file + rename) to prevent corruption
3. Preserves existing tags, types, and metadata from the original JSON structure
4. Ensures the data directory exists before writing

Acceptance Criteria

• add_memory persists new memories to disk
• update_memory persists changes to disk
• delete_memory persists deletions to disk
• File writes are atomic (no partial writes on failure)
• Original JSON structure (tags, types, metadata) is preserved