docs(infra): correct server specs — Hetzner Serverbörse i7-6700 64 GB, not CX32

Replace all references to the CX32 VPS (8 GB RAM, Hetzner Cloud) with the
actual production server: a Hetzner Serverbörse dedicated server with an
Intel Core i7-6700 (4C/8T, 3.4 GHz) and 64 GB RAM.

Affected files:
- .claude/personas/devops.md — monthly cost line + upgrade example
- docs/infrastructure/production-compose.md — sizing section + cost table
- docs/DEPLOYMENT.md — OCR memory table + OCR_MEM_LIMIT env var description
- docs/adr/004-pdfbox-thumbnails.md — thumbnailExecutor memory ceiling note
- docs/adr/021-tmpdir-persistent-volume-staging.md — OOMKill rationale in alternatives

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/personas/devops.md

@@ -154,9 +154,9 @@ Schedule monthly automated restore tests. If the restore fails, the backup is wo
 ```
 Every alert needs: description, severity, likely cause, resolution steps, escalation path.
 
-3. **Upgrading VPS tier before profiling**
+3. **Upgrading hardware before profiling**
 ```
-# "The app feels slow" → upgrade from CX32 to CX42
+# "The app feels slow" → order more RAM / a faster CPU
 # Actual cause: unindexed query scanning 100k rows
 ```
 Profile with Grafana dashboards first. Most perceived performance issues are application bugs, not resource constraints.
@@ -404,8 +404,8 @@ Hetzner Object Storage (S3-compatible, replaces MinIO in prod)
 Prometheus + Loki + Alertmanager
 ```
 
-### Monthly Cost: ~23 EUR
-CX32 VPS (4 vCPU, 8GB RAM): 17 EUR · Object Storage (~200GB): 5 EUR · SMTP relay: ~1 EUR
+### Monthly Cost: ~6 EUR (excl. server)
+Hetzner dedicated server (Serverbörse, i7-6700, 64 GB RAM): see invoice · Object Storage (~200GB): 5 EUR · SMTP relay: ~1 EUR
 
 ### Reference Documentation
 - Full CI workflow, Gitea vs GitHub differences: `docs/infrastructure/ci-gitea.md`