Overhaul run.sh scripts

- Default environment variables through this, instead of .env
- Added some basic checks to ensure developers don't stub their toe
- Use `railway link`, injecting environment variables without insecure dotenv files

frontend/run.sh

@@ -1,3 +1,10 @@
 #!/usr/bin/env bash
 
+# Check whether CWD is 'frontend'
+if [ "$(basename "$(pwd)")" != "frontend" ]; then
+    echo "error: This script must be run from the 'frontend' directory."
+    exit 1
+fi
+
+export VITE_BACKEND_TARGET=${VITE_BACKEND_TARGET:-localhost:8000}
 pnpm run dev