PR AB: complete Phoenix deployment scaffolding (add 3 files referenced by main 4a1f69a) (#32)

Adds webapp-nginx.conf, systemd/currencicombo-orchestrator.service, and install-prune-cron.sh — all three referenced by main's existing install.sh / deploy script / webapp.service / README but missing from the 4a1f69a commit. Byte-identical to PR #31 branch ded7d24.

Closes gap so CT 8604 can boot cleanly.

scripts/deployment/webapp-nginx.conf

@@ -0,0 +1,80 @@
+# Self-contained nginx.conf for the CurrenciCombo Vite SPA.
+# Invoked by the `currencicombo-webapp.service` systemd unit and installed
+# to /etc/currencicombo/webapp-nginx.conf by scripts/deployment/install.sh.
+#
+# Listens on :3000 (NPMplus upstream). NPMplus path-routes /api/* to the
+# orchestrator on :8080 (with SSE-friendly settings — see README.md);
+# everything else lands here.
+# This config does NOT proxy /api itself — that's intentional so a wrong
+# NPMplus rule fails loudly instead of silently bypassing the orchestrator.
+
+worker_processes auto;
+error_log /var/log/currencicombo/webapp-nginx.error.log warn;
+
+events {
+  worker_connections 1024;
+}
+
+http {
+  include /etc/nginx/mime.types;
+  default_type application/octet-stream;
+
+  access_log /var/log/currencicombo/webapp-nginx.access.log combined;
+
+  sendfile on;
+  tcp_nopush on;
+  keepalive_timeout 65;
+  server_tokens off;
+  gzip on;
+  gzip_types text/plain text/css application/javascript application/json image/svg+xml;
+  gzip_min_length 1024;
+
+  # Uploads/bodies: the portal is a static SPA, so any request with a body
+  # is almost certainly mis-routed. Cap tight.
+  client_max_body_size 1m;
+
+  server {
+    listen 3000 default_server;
+    listen [::]:3000 default_server;
+    server_name _;
+
+    root /opt/currencicombo/webapp/dist;
+    index index.html;
+
+    # Security headers are also set by NPMplus, but apply them here too
+    # so they survive a direct-to-CT curl for debugging.
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+
+    # Immutable asset bundles.
+    location /assets/ {
+      access_log off;
+      expires 1y;
+      add_header Cache-Control "public, max-age=31536000, immutable";
+      try_files $uri =404;
+    }
+
+    # Deny sourcemaps in prod.
+    location ~ \.map$ {
+      access_log off;
+      deny all;
+      return 404;
+    }
+
+    # Guard-rail: if NPMplus fails to path-route /api/*, surface it as a
+    # clean 421 rather than serving index.html and confusing the browser
+    # with a JSON parse error. The SSE endpoint lives at
+    # /api/plans/:id/events/stream, which also sits under /api/, so one
+    # rule covers both.
+    location /api/ {
+      return 421 "NPMplus is misconfigured: /api/* must proxy to orchestrator :8080\n";
+      add_header Content-Type text/plain always;
+    }
+
+    # SPA fallback. Must come last.
+    location / {
+      try_files $uri $uri/ /index.html;
+    }
+  }
+}