chore: add .dockerignore (completes the tracked Docker setup)

Excludes node_modules/dist (rebuilt in-image; host copies are Windows-native),
.git, .env and data — matching the existing Dockerfile + docker-compose.yml.

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

.dockerignore

@@ -0,0 +1,9 @@
+# Keep the build context small and correct. node_modules and dist are rebuilt inside
+# the image (host copies are Windows/native-built and would break Linux); .env and data
+# must never be baked into an image.
+**/node_modules
+**/dist
+.git
+**/.env
+**/data
+*.log