Ship container/app logs to Loki via an alloy Fleet Management pipeline

## Summary
Add an alloy pipeline (Terraform-defined Fleet Management pipeline) that tails the Docker container logs and ships them to Loki, so per-app stdout/stderr is searchable in Grafana alongside host logs.

## Motivation
Host service logs already reach Loki via syslog-forward, but individual container stdout does not. TrueNAS Docker uses the `json-file` log driver (container logs on disk), and the journald route is a dead end — SCALE overwrites `/etc/docker/daemon.json` on reboot. So alloy must tail the files.

## Scope
- alloy `loki.source.file` tailing `.ix-apps/docker/containers//-json.log` -> Loki.
- Relabel container-id -> app name; drop noisy sources (Plex can be chatty) for ingestion cost.
- Authored as a Fleet Management pipeline in Terraform.

## Acceptance criteria
- [ ] Per-container app logs appear in Loki, labeled by app.
- [ ] Plex/noisy chatter filtered to control Grafana Cloud ingestion.

Blocked by #150 (Fleet Management foundation).