Replace parted resizepart with sfdisk --force

parted fails to resize a mounted partition non-interactively.
sfdisk --no-reread --force writes the updated partition table
directly without TTY/confirmation issues, and partprobe
re-reads it afterwards.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

system_setup/install.sh

@@ -377,9 +377,16 @@ if [[ "$MODE" == "shrink" ]]; then
     fi
 
     info "Shrinking partition $S_PNUM to ${NEW_END} MiB in partition table..."
-    # Use printf instead of -s so parted's "partition is busy" confirmation is answered Yes
-    printf 'Yes\n' | parted "$S_DISK" resizepart "$S_PNUM" "${NEW_END}MiB" \
-        || die "parted resizepart failed."
+    SECTOR_SIZE=$(cat /sys/block/"${S_DISK##*/}"/queue/hw_sector_size 2>/dev/null || echo 512)
+    NEW_END_SEC=$(( NEW_END * 1048576 / SECTOR_SIZE ))
+    sfdisk -d "$S_DISK" | awk -v dev="$S_DEV" -v new_end="$NEW_END_SEC" '
+        $0 ~ "^" dev " : " {
+            match($0, /start= *([0-9]+)/, a)
+            sub(/size= *[0-9]+/, "size= " (new_end - a[1]+0))
+        }
+        { print }
+    ' | sfdisk --no-reread --force "$S_DISK" \
+        || die "sfdisk partition resize failed."
 fi
 
 # ── Create OEMDRV partition ───────────────────────────────────────────────────