feat(journal): surface Fedify logs via LogTape console sink

Inbound Mastodon Follows are being rejected 401 (signature
verification) on staging and Fedify's diagnostics were invisible:
it logs through LogTape, which is silent until configured.

- Configure LogTape with a console sink for the 'fedify' category when
  the federation instance is built; level via FEDERATION_LOG_LEVEL
  (default info).
- Staging deploy sets FEDERATION_LOG_LEVEL=debug for the soak —
  signature-verification detail per request; dial down once proven.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

infrastructure/docker-compose.staging.yml

@@ -66,6 +66,7 @@ services:
       # empty (flag off) so preview journals never emit federation traffic.
       FEDERATION_ENABLED: ${FEDERATION_ENABLED:-}
       FEDERATION_KEY_ENCRYPTION_KEY: ${FEDERATION_KEY_ENCRYPTION_KEY:-}
+      FEDERATION_LOG_LEVEL: ${FEDERATION_LOG_LEVEL:-}
     healthcheck:
       test: ["CMD-SHELL", "curl -sf http://localhost:3000/api/health || exit 1"]
       interval: 15s