add FPM worker tuning and architecture diagram

Increase PHP-FPM max_children from 5 to 12 to handle concurrent
requests without queuing, sized for a ~3GB VPS. Add Mermaid
architecture diagram to README.

README.md

@@ -2,6 +2,48 @@
 
 Docker Compose setup for a self-hosted VPS running Nextcloud, Gitea, and monitoring — managed as a GitOps-style repo.
 
+## Architecture
+
+```mermaid
+graph TB
+    Internet([Internet])
+
+    subgraph VPS["VPS (t-gstone.de)"]
+        subgraph proxy_net["proxy network"]
+            Caddy["Caddy<br/>reverse proxy + auto HTTPS"]
+        end
+
+        subgraph nc_stack["Nextcloud Stack"]
+            Nginx["Nginx<br/>static files + FastCGI proxy"]
+            NC["Nextcloud FPM<br/>PHP processing"]
+            Cron["Cron<br/>background jobs"]
+            PG["PostgreSQL 17"]
+            Redis["Redis 8"]
+        end
+
+        subgraph gitea_stack["Gitea Stack"]
+            Gitea["Gitea<br/>rootless, SQLite"]
+        end
+
+        subgraph mon_stack["Monitoring Stack"]
+            Alloy["Grafana Alloy"]
+        end
+    end
+
+    GrafanaCloud([Grafana Cloud])
+
+    Internet -->|":443 HTTPS"| Caddy
+    Internet -->|":2222 SSH"| Gitea
+    Caddy -->|"nextcloud.t-gstone.de"| Nginx
+    Caddy -->|"git.t-gstone.de"| Gitea
+    Nginx -->|":9000 FastCGI"| NC
+    NC --> PG
+    NC --> Redis
+    Cron --> PG
+    Cron --> Redis
+    Alloy -->|"logs + metrics"| GrafanaCloud
+```
+
 ## Prerequisites
 
 - A VPS with SSH access

nextcloud/docker-compose.yml

@@ -19,6 +19,7 @@ services:
       - ${DATA_ROOT}/nextcloud/data:/var/www/html/data
       - ./hooks/post-installation.sh:/docker-entrypoint-hooks.d/post-installation/post-installation.sh:ro
       - ./hooks/post-upgrade.sh:/docker-entrypoint-hooks.d/post-upgrade/post-upgrade.sh:ro
+      - ./fpm-tuning.conf:/usr/local/etc/php-fpm.d/zz-tuning.conf:ro
     networks:
       - nextcloud-internal
     logging:

nextcloud/fpm-tuning.conf

@@ -0,0 +1,7 @@
+[www]
+pm = dynamic
+pm.max_children = 12
+pm.start_servers = 4
+pm.min_spare_servers = 2
+pm.max_spare_servers = 6
+pm.max_requests = 500