Fix service disable mechanism to allow retry on failure

[Copilot]

The grow-ssd service used an unconditional trap that disabled the service even when partition growth failed, preventing automatic retry on reboot.

Changes

• Removed unconditional trap - Deleted trap 'sv down ...' 0 that executed on any exit
• Added explicit disable on success - Call sv down only after:
  • Successful completion of growpart + resize2fs
  • Intentional no-op exits (device not found, no partition, no growth needed)
• Enable retry on failure - If growpart/resize2fs fail, service remains enabled due to set -e exiting before sv down

Example

Before:

trap 'sv down /var/service/grow-ssd >/dev/null 2>&1 || true' 0  # Always disables
growpart "$DISK" "$PART"  # Failure still triggers trap

After:

growpart "$DISK" "$PART"  # Failure exits here, service stays enabled
resize2fs "$SSD_DEV"
sv down /var/service/grow-ssd >/dev/null 2>&1 || true  # Only reached on success

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