[ARI-31] End-to-end integration test — full pipeline

[bjridicodes]

Linear: ARI-31

Type: ⚙️ Enabler | Sprint: 6 | Points: 3 | AC: AC-01

As a Data Platform OPS engineer, I want an integration test that runs the complete pipeline from incident ingestion to Slack notification so that all agent interactions are validated together before acceptance testing.

Acceptance Criteria

Given the 3 fixture incidents and in-memory implementations
When the full pipeline runs in dry-run mode for each incident
Then all 3 complete without exceptions and produce a notification payload

Given the integration test for INC0000001 (cdp-worker-03 disk full)
When the pipeline completes
Then the classification error_class is "disk_full" or similar
And the notification_sent flag in PipelineState is True

Given all 3 integration tests run
When execution time is measured per incident
Then each completes in under 60 seconds (AC-01 baseline)