feat(docker): add containerized nginx deployment with runtime base path

Two-stage build: node builds the static bundle, nginx serves it. The bundle is
built against a placeholder base token that the entrypoint rewrites to $BASE_URL
at start, so one image serves from any path without a rebuild.

nginx config caches hashed assets forever, never caches index.html, and applies
security headers (CSP, no framing, no referrer) suited to an app that handles
cloud credentials client-side.

.gitattributes pins LF on the container-consumed files, since core.autocrlf
would otherwise give the entrypoint a CRLF shebang.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,11 @@
+services:
+  ready2blob:
+    build: .
+    image: ready2blob:latest
+    container_name: ready2blob
+    ports:
+      - "8080:80"
+    environment:
+      # "/" for a dedicated (sub)domain; "/ready2blob/" to mount under a path.
+      BASE_URL: "/"
+    restart: unless-stopped