fix(images): normalize shell scripts to LF line endings

database image crashed at start: CRLF shebang in start.sh made the kernel
look for interpreter '/bin/bash\r'. Other image Dockerfiles mask this with
dos2unix at build time, but scripts/images/database/Dockerfile does not.
Convert all tracked .sh files to LF and pin eol=lf via .gitattributes.

scripts/images/backend/start.sh

@@ -1,8 +1,8 @@
-#!/bin/bash
-
-set -e
-
-umask 0022
-
-echo "Starting main application..."
-exec "$@"
+#!/bin/bash
+
+set -e
+
+umask 0022
+
+echo "Starting main application..."
+exec "$@"