[Epic] Graph quality and inference

[imsouza]

Owner: @imsouza

Outcome:
Maintain useful nodes and explainable edges, grounded inference, graph integrity, and reversible actions.

Acceptance criteria:

• Scope is implemented with persisted, non-mock data where applicable.
• Success, empty, degraded, and failure states are covered.
• Automated tests and documentation are updated.
• Evidence is attached before closure.