feat: add analytics event schema registry with emit-time validation - #985

Overview

This PR adds a versioned Analytics Event Schema Registry with emit-time validation for the backend analytics pipeline. Every analytics event now declares a schema in a central registry, events are validated before they are recorded, invalid events are rejected and counted, and the registry is exported in a machine-readable form that dashboards and downstream consumers can read. Breaking schema changes are caught in CI unless the schema version is incremented.

Related Issue

Changes

🧩 Schema Registry & Validation

• [MODIFY] app/backend/src/analytics/analytics.service.ts

  • Introduces a central, versioned schema registry keyed by event name and schema version.
  • Validates every event against its declared schema at emit time; rejects malformed events instead of recording them.
  • Tracks rejected/invalid events with a counter for observability.
  • Emits a validation error path so producers get immediate, actionable feedback.

• [MODIFY] app/backend/src/analytics/analytics.module.ts

  • Wires the registry and export service into the analytics module and exposes them for injection.

• [ADD] app/backend/src/analytics/schema-export.service.ts

  • Exports the full registry (event names, versions, field definitions) in a consumer-readable form for dashboards and downstream consumers.
  • Provides a stable snapshot used by CI to detect breaking changes.

• [ADD] CI compatibility guard

  • Compares the committed schema snapshot against the current registry; adding a required field or removing a field fails CI unless the schema version is incremented.

• [ADD] Tests

  • Coverage for schema validation, rejection + counting of invalid events, registry export shape, and the version-bump CI guard.

Verification Results

npm test -- src/analytics
✅ 12/12 passed

Live acceptance check:
✅ All emitted events validated against a versioned schema
✅ Invalid events rejected and counted (rejection counter increments)
✅ Breaking change without version bump fails CI guard
✅ Registry export readable by dashboards/consumers

Closes #822