[ai] Add prompt and output logging with PII filtering

[NUMBER72857]

Imported from docs/github-issues-backlog.md.

Scope:

• [ai] Add prompt and output logging with PII filtering

Acceptance criteria:

• Implementation is covered by tests or an explicit manual verification note.
• Money-state behavior is idempotent where applicable.
• Logs and audit events avoid leaking PII or secrets.
• Documentation or runbook updates are included when operator behavior changes.