fix(mission): 修复回合开始前未选英雄直接开战的问题

调整关卡战斗阶段切换逻辑，新增MissionPhase.Battle相位守卫，避免未选择英雄就自动进入战斗导致玩家判负；同时调整mission.prefab的UI布局参数适配新逻辑

assets/resources/gui/element/mission.prefab

@@ -3131,7 +3131,7 @@
     "_lpos": {
       "__type__": "cc.Vec3",
       "x": 0,
-      "y": 589.929,
+      "y": 902.919,
       "z": 0
     },
     "_lrot": {
@@ -3588,7 +3588,7 @@
     "_lpos": {
       "__type__": "cc.Vec3",
       "x": 0,
-      "y": 331.679,
+      "y": 644.669,
       "z": 0
     },
     "_lrot": {
@@ -3661,7 +3661,7 @@
     "_top": 535,
     "_bottom": 645,
     "_horizontalCenter": 0,
-    "_verticalCenter": -308.321,
+    "_verticalCenter": 4.668999999999983,
     "_isAbsLeft": true,
     "_isAbsRight": true,
     "_isAbsTop": true,
@@ -3766,7 +3766,7 @@
     "_lpos": {
       "__type__": "cc.Vec3",
       "x": 0,
-      "y": 70.17200000000003,
+      "y": 383.162,
       "z": 0
     },
     "_lrot": {
@@ -4620,7 +4620,7 @@
     "_top": 340.279,
     "_bottom": -521.315,
     "_horizontalCenter": 0,
-    "_verticalCenter": -569.828,
+    "_verticalCenter": -256.838,
     "_isAbsLeft": true,
     "_isAbsRight": true,
     "_isAbsTop": true,
@@ -5384,8 +5384,8 @@
     },
     "_lpos": {
       "__type__": "cc.Vec3",
-      "x": 230,
-      "y": 1110,
+      "x": 0,
+      "y": 980,
       "z": 0
     },
     "_lrot": {
@@ -6711,11 +6711,11 @@
     "__prefab": {
       "__id__": 320
     },
-    "_alignFlags": 33,
+    "_alignFlags": 17,
     "_target": null,
     "_left": 310,
     "_right": 30,
-    "_top": 20,
+    "_top": 150,
     "_bottom": 638.669,
     "_horizontalCenter": 0,
     "_verticalCenter": 0,
@@ -6868,7 +6868,6 @@
     "time_label": {
       "__id__": 305
     },
-    "phase_label": null,
     "tooltip": {
       "__id__": 240
     },