[DhruvGarg111]

Summary

• centralize the nine-field KnowledgeEntry mapping in shared JSON-shaped serialization helpers
• use the shared mapping across file, SQLite, Redis, and Supabase stores while preserving each backend's wire format
• coerce importance consistently to float, including legacy SQLite rows, and normalize nullable defaults
• add regression and round-trip coverage for every affected backend

Testing

• python -m ruff format --check on all modified Python files
• python -m ruff check on all modified Python files
• focused knowledge-store suite: 116 passed
• architecture suite: 1,194 passed

Closes #145