fix: 修复 apt 升级后服务需要手动重新启用的问题

- 修改 prerm 脚本，升级时只停止服务不禁用
- 修改 postinst 脚本，升级后自动重启已启用的服务
- 首次安装仍保持手动启用服务的行为

debian/prerm

@@ -1,17 +1,33 @@
-#!/bin/sh
-set -e
+case "$1" in
+    upgrade)
+        # Stop service only during upgrade, keep enabled state
+        if [ -d /run/systemd/system ]; then
+            if systemctl is-active --quiet p2pool.service; then
+                echo "Stopping p2pool service for upgrade..."
+                systemctl stop p2pool.service
+            fi
+        fi
+        ;;
+    remove|deconfigure)
+        # Stop and disable service during removal
+        if [ -d /run/systemd/system ]; then
+            if systemctl is-active --quiet p2pool.service; then
+                echo "Stopping p2pool service..."
+                systemctl stop p2pool.service
+            fi
+            if systemctl is-enabled --quiet p2pool.service 2>/dev/null; then
+                echo "Disabling p2pool service..."
+                systemctl disable p2pool.service
+            fi
+        fi
+        ;;
+    failed-upgrade)
+        # Do nothing on failed upgrade
+        ;;
+    *)
+        echo "prerm called with unknown argument \`$1'" >&2
+        exit 1
+        ;;
+esac
 
-# Stop and disable service if running
-if [ -d /run/systemd/system ]; then
-    if systemctl is-active --quiet p2pool.service; then
-        echo "Stopping p2pool service..."
-        systemctl stop p2pool.service
-    fi
-
-    if systemctl is-enabled --quiet p2pool.service 2>/dev/null; then
-        echo "Disabling p2pool service..."
-        systemctl disable p2pool.service
-    fi
-fi
-
-exit 0
+exit 0