Sync & Privacy Foundation + CI Fix

[google-labs-jules]

This PR addresses the user request to fix the CI failure badge and start implementing the Sync & Privacy roadmap.

1. CI Fix:

   • Identified that isar_agent_memory_tests was missing isar_flutter_libs, causing tests to fail on finding the Isar library.
   • Added the missing dependency and verified tests pass locally.

2. Sync & Privacy (Phase 1):

   • Added cryptography package (avoiding encrypt/pointycastle conflicts).
   • Implemented EncryptionService using AesGcm (AES-256-GCM).
   • Added SyncManager class (skeleton).
   • Extended MemoryNode and MemoryEdge with fields required for LWW sync: modifiedAt, version, deviceId, isDeleted.

3. Modernization:

   • Researched HiRAG (Hierarchical RAG).
   • Checked dependencies (updated via flutter pub outdated findings where safe).

This lays the groundwork for full multi-device synchronization in future releases.

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PR created automatically by Jules for task 6694733581578485995 started by @iberi22

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