Add backup shrinking functionality to eMMC provisioning dashboard: implement API for shrinking raw .img backups using PiShrink, update UI to support shrink option after backup, and enhance documentation for backup image handling and storage options on Proxmox host.

chromium-setup/emmc-provisioning/cloud-init/user-data-remote-bootstrap.example

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+#cloud-config
+# Example user-data that downloads and runs a script from a file server.
+# Use this so you can change first-boot behaviour without rebuilding the golden image.
+# Copy to boot partition as 'user-data' and set BOOTSTRAP_URL to your script URL.
+
+package_update: true
+package_upgrade: false
+
+packages:
+  - curl   # or wget if you prefer
+
+# Download script from file server and run it (runcmd runs after network is up)
+runcmd:
+  - curl -fsSL "http://YOUR_FILE_SERVER/provisioning/bootstrap.sh" -o /tmp/bootstrap.sh
+  - chmod +x /tmp/bootstrap.sh
+  - /tmp/bootstrap.sh
+  # Optional: remove after run
+  # - rm -f /tmp/bootstrap.sh
+
+# Optional: finish cloud-init
+# - cloud-init single --name cc_final_message