fix: log fetches and mutation intents

[eshaffer321]

Summary

• add provider_fetches audit table for provider/Monarch fetch request and response snapshots
• add api_calls.phase so mutation intent is recorded before Monarch writes and completion is recorded afterward
• log provider order fetches, Monarch transaction discovery, and category loading with run IDs
• start sync runs before external fetches so fetch audit rows are tied to a run

Verification

• go test ./...
• go build -o itemize ./cmd/itemize/

Stacking

This is stacked on #60 (codex/audit-costco-reconciliation) because it builds on the audit schema added there. After #60 merges, this PR can be retargeted/rebased onto main.