fix: replace fragile printf start.sh with COPY start.sh

The RUN printf approach had a POSIX printf bug where \\c stopped
output, truncating the startup script. Now start.sh is a proper
file COPYed into the image.

start.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+# Falah Mobile — container startup script
+cd /app
+# Run Prisma migrations against the volume-mounted DB
+node ./node_modules/prisma/build/index.js db push --skip-generate --accept-data-loss 2>&1
+# Force 0.0.0.0 binding (Docker sets HOSTNAME to container ID)
+export HOSTNAME=0.0.0.0
+exec node server.js