feat(api): expose Ego Portal E2 conversion operations

[shark0F0497]

Summary

• expose single-Episode E2 conversion operations through Data Ops APIs
• add get, process, retry, cancel, logs, and retry-QA endpoints
• add E2 processing settings and settings-history endpoints
• wire the existing E2 conversion Manager into DataOpsHandler
• keep E2 cloud sync on the ordinary Episode sync entrypoint; no E2-specific sync API is added
• add consistent E2-specific HTTP error mapping

Endpoints

GET  /api/v1/data-ops/episodes/:id/derivatives/e2-multimodal-conversion
POST /api/v1/data-ops/episodes/:id/derivatives/e2-multimodal-conversion/process
POST /api/v1/data-ops/episodes/:id/derivatives/e2-multimodal-conversion/retry
POST /api/v1/data-ops/episodes/:id/derivatives/e2-multimodal-conversion/cancel
GET  /api/v1/data-ops/episodes/:id/derivatives/e2-multimodal-conversion/logs
POST /api/v1/data-ops/episodes/:id/derivatives/e2-multimodal-conversion/qa
GET  /api/v1/data-ops/processing-settings/e2-multimodal-conversion
PUT  /api/v1/data-ops/processing-settings/e2-multimodal-conversion
GET  /api/v1/data-ops/processing-settings/e2-multimodal-conversion/history

Validation

• gofmt
• go test ./...
• git diff --check

Scope

This PR provides the backend Data Ops API. Synapse UI remains in PR8.