docs: native Ubuntu install as primary; systemd and nginx

- install-ubuntu-24.04-native.md (production) and -docker.md (alternative)

- deploy/systemd/sac-api.service, nginx/sac.conf.example, env.native.example

- deployment, README, INDEX, work-plan, TZ updated

deploy/nginx/sac.conf.example

@@ -0,0 +1,44 @@
+# /etc/nginx/sites-available/sac
+# Замените sac.example.com на ваш FQDN.
+# API слушает только 127.0.0.1:8000 (systemd sac-api).
+
+upstream sac_api {
+    server 127.0.0.1:8000;
+    keepalive 8;
+}
+
+server {
+    listen 80;
+    listen [::]:80;
+    server_name sac.example.com;
+
+    location /.well-known/acme-challenge/ {
+        root /var/www/html;
+    }
+
+    location / {
+        return 301 https://$host$request_uri;
+    }
+}
+
+server {
+    listen 443 ssl http2;
+    listen [::]:443 ssl http2;
+    server_name sac.example.com;
+
+    # После certbot пути подставятся автоматически, либо укажите вручную:
+    # ssl_certificate     /etc/letsencrypt/live/sac.example.com/fullchain.pem;
+    # ssl_certificate_key /etc/letsencrypt/live/sac.example.com/privkey.pem;
+
+    client_max_body_size 2m;
+
+    location / {
+        proxy_pass http://sac_api;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        proxy_read_timeout 60s;
+    }
+}