Add rebuildable vector memory and harden migration surfaces

[EricSun0218]

Summary

• add optional model-agnostic vector memory with hybrid recall, rebuild diagnostics, and game-aware reranking
• expose stable local-source integration for Godot and bump active package surfaces to 0.3.0-alpha.2
• replace ephemeral run-derived persistent identifiers with replay-stable canonical identities
• harden real Godot editor smoke validation and same-version NuGet repacking
• remove stale local legacy package artifacts from the verified integration path

Verification

• full Release solution tests pass
• Godot 4.7.1 .NET and Unity 6000.5.6f1 real-editor smoke tests pass
• all 23 NuGet packages rebuild with the same repository commit
• clean consumer restores and builds all 23 packages
• public-tree and release-script gates pass