fix(api): decode memory observation scopes

[Jordan-Jarvis]

Summary

• deserialize the JSONB observation_scopes column before returning memory detail/update responses
• preserve named modes such as shared and explicit tag-group arrays as native JSON values
• extend the existing invalidation regression to cover the archived memory response shape

Why

The PostgreSQL adapter returns JSONB as encoded JSON text. get_memory_unit() already deserializes other JSON columns but returned observation_scopes directly. A stored shared mode was therefore emitted as the JSON string "\"shared\"" rather than "shared". Strict OpenAPI-compatible clients reject that response after update/invalidation succeeds.

The fix is at the database/API producer boundary and uses the existing backend-aware JSON deserializer, preserving both PostgreSQL and Oracle behavior.

Validation

• existing PostgreSQL curation/invalidation regression passed with observation_scopes="shared"
• Ruff check passed
• Ruff format check passed