add dockerignore for backend and frontend dev images.

Prevent copying host node_modules, dist, and build artifacts into Docker build context.

backend/.dockerignore

@@ -0,0 +1,10 @@
+node_modules
+npm-debug.log
+dist
+*.tsbuildinfo
+.git
+.gitignore
+Dockerfile*
+coverage
+*.local
+uploads

frontend/.dockerignore

@@ -0,0 +1,6 @@
+node_modules
+dist
+.git
+.gitignore
+Dockerfile*
+npm-debug.log