build: add Fly.io deployment (nginx static serving)

- Dockerfile: serve the static PWA via nginx:alpine on port 8080
- deploy/nginx.conf: mirror .htaccess (jsx/mjs MIME, no-cache for shell/sw/manifest/meta/dist,
  long-immutable cache for assets, security headers, SPA fallback)
- fly.toml: internal_port 8080, force_https, scale-to-zero
- .dockerignore: exclude .git/node_modules/tests from the image

.dockerignore

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+.git
+.github
+node_modules
+tools
+tests
+Dockerfile
+.dockerignore
+fly.toml
+*.log
+.DS_Store
+**/.DS_Store

Dockerfile

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+# SecureBit.chat is a static PWA (no backend). The committed build artifacts in
+# dist/ are served as-is by nginx — matching the project's release workflow,
+# where dist/ is rebuilt and committed for every release.
+FROM nginx:1.27-alpine
+
+# Replace the default nginx config with our static-serving config.
+COPY deploy/nginx.conf /etc/nginx/nginx.conf
+
+# Serve the repository (src/, assets/, libs/, dist/, config/, logo/, sw.js, ...).
+COPY . /usr/share/nginx/html
+
+# Fly.io health checks and routing target this port.
+EXPOSE 8080
+
+CMD ["nginx", "-g", "daemon off;"]

deploy/nginx.conf

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+# nginx config for serving SecureBit.chat (static PWA) on Fly.io.
+# Mirrors the behavior of the Apache .htaccess: correct JS MIME for ES modules
+# (.jsx/.mjs), no-cache for the app shell / service worker / versioning files,
+# long-immutable cache for hashed/static assets, security headers, SPA fallback.
+
+worker_processes auto;
+events { worker_connections 1024; }
+
+http {
+    include       /etc/nginx/mime.types;
+    default_type  application/octet-stream;
+
+    # ES modules must be served as JavaScript. nginx's default mime.types maps
+    # .js but not .mjs/.jsx — declare them explicitly (this overrides .js too).
+    types {
+        application/javascript  js mjs jsx;
+        text/css                css;
+        application/json        json map;
+        application/manifest+json webmanifest;
+        font/woff2              woff2;
+        font/woff               woff;
+        image/svg+xml           svg;
+    }
+
+    sendfile      on;
+    tcp_nopush    on;
+    server_tokens off;
+
+    gzip            on;
+    gzip_vary       on;
+    gzip_min_length 256;
+    gzip_types      text/plain text/css application/javascript application/json image/svg+xml font/woff2;
+
+    # Decide Cache-Control from the request path. Keeping all add_header calls at
+    # one level avoids nginx's header-inheritance reset between blocks.
+    map $uri $sb_cache {
+        default                  "public, max-age=31536000, immutable";
+        ~^/index\.html$          "no-cache, no-store, must-revalidate";
+        ~^/$                     "no-cache, no-store, must-revalidate";
+        ~^/sw\.js$               "no-cache, no-store, must-revalidate";
+        ~^/manifest\.json$       "no-cache, no-store, must-revalidate";
+        ~^/meta\.json$           "no-cache, no-store, must-revalidate";
+        ~^/dist/                 "no-cache, no-store, must-revalidate";
+    }
+
+    server {
+        listen      8080;
+        listen      [::]:8080;
+        server_name _;
+        root        /usr/share/nginx/html;
+        index       index.html;
+
+        # Security headers (frame-ancestors complements the in-page CSP meta tag).
+        add_header X-Content-Type-Options   "nosniff"                          always;
+        add_header Referrer-Policy          "strict-origin-when-cross-origin"  always;
+        add_header X-Frame-Options          "DENY"                             always;
+        add_header Content-Security-Policy   "frame-ancestors 'none';"         always;
+        add_header Cache-Control            $sb_cache                          always;
+        add_header Service-Worker-Allowed   "/"                                always;
+
+        # SPA-style fallback so unknown routes still load the app shell.
+        location / {
+            try_files $uri $uri/ /index.html;
+        }
+    }
+}

fly.toml

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+# Fly.io configuration for SecureBit.chat (static PWA served by nginx).
+# Set `app` to your chosen Fly app name and `primary_region` to the closest
+# region (e.g. fra=Frankfurt, ams=Amsterdam, waw=Warsaw, iad=US East).
+# Run `fly platform regions` to list them.
+
+app = "securebit-chat"
+primary_region = "fra"
+
+[build]
+  dockerfile = "Dockerfile"
+
+[http_service]
+  internal_port = 8080
+  force_https = true            # matches the app's upgrade-insecure-requests CSP
+  auto_stop_machines = "stop"
+  auto_start_machines = true
+  min_machines_running = 0      # scale to zero when idle (free-tier friendly)
+
+  [http_service.concurrency]
+    type = "requests"
+    soft_limit = 200
+    hard_limit = 250
+
+[[vm]]
+  size = "shared-cpu-1x"
+  memory = "256mb"