feat: Grafana Loki log adapter for ingestion

[leo-aa88]

Summary

Add a Loki ingestion adapter so logs can be queried from Loki (LogQL) and written through the same ParsedLogLine → storage pipeline as file ingest.

Motivation

• README Roadmap lists a Loki adapter.
• Common in Kubernetes / Grafana Cloud deployments.

Scope (proposal)

• Adapter that queries Loki HTTP API for a time range and maps stream labels + line to ParsedLogLine.
• CLI or unified ingest flags for Loki base URL, tenant, auth (Bearer / basic), LogQL query, --since / --from/--to alignment with existing window UX.
• Env-based config (URL, auth, default query).

Acceptance criteria

• Bounded window ingest from Loki into Postgres without intermediate files.
• Tests with mocked Loki responses.

References

• Loki HTTP API: https://grafana.com/docs/loki/latest/reference/loki-http-api/