[F2-TASK-160] Add tier-2 stage performance baselines

[duksh]

Execution Metadata

• Issue ID: F2-TASK-160
• Phase: P13
• Type: TASK
• Owner Team: qa-team
• Priority: P2
• Status (initial): Todo
• Depends On: F2-STORY-157

Acceptance Criteria

Latency and ingest success baselines documented

Artifact Paths

• docs/billing-direct-integration-contract.md

Quality Gates

• contract-drift

Labels (from registry)

performance,tier2

Source Registry

• docs/roadmap/ficecal-v2-task-issue-registry.csv
• docs/roadmap/ficecal-v2-execution-plan-updated.md
• docs/roadmap/ficecal-v2-recovery-index.md