feat(cma): strategy map lane KR delete entry (cma-map-kr-delete-entry-20260916)

- MapNode.vue: hover trash icon per KR row emitting delete-kr (inline SVG, no emoji)

- StrategyLayer.vue / MapCanvas.vue: passthrough + MyDialog second confirm + okrApi.deleteKr + whole-map save

- MapsDialog: single-KR policy hint (keep at least 1 KR per objective)

frontend/src/components/map-canvas/MapCanvasDialogs.vue

@@ -61,7 +61,10 @@
 
       <div class="mc-kr-section">
         <div class="mc-kr-header">
-          <span>关键结果（{{ form.krs.length }}条）</span>
+          <span>
+            关键结果（{{ form.krs.length }}条）
+            <span class="mc-kr-min-hint">每个目标至少保留 1 条</span>
+          </span>
           <span style="display:flex;gap:6px;">
             <el-button size="small" plain @click="autoDivideWeights">⚖️ 自动平分</el-button>
             <el-button size="small" type="primary" plain @click="addKr">+ 添加KR</el-button>
@@ -72,7 +75,7 @@
           <div class="mc-kr-row-top">
             <span class="mc-kr-index">#{{ ki + 1 }}</span>
             <input v-model="kr.name" class="mc-input mc-kr-name" placeholder="KR名称" />
-            <el-button v-if="form.krs.length > 1" size="small" text type="danger" @click="removeKr(ki)">×</el-button>
+            <el-button v-if="form.krs.length > 1" size="small" text type="danger" title="删除该关键结果" @click="removeKr(ki)">×</el-button>
           </div>
           <div class="mc-kr-row-bottom">
             <div class="mc-kr-field">
@@ -937,6 +940,13 @@ function planStatusLabel(s: string): string {
   font-weight: 500;
   color: #606266;
 }
+/* 单条 KR 口径提示（2026-09-16）：不允许删到 0，UI 明示 */
+.mc-kr-min-hint {
+  margin-left: 8px;
+  font-size: 11px;
+  font-weight: 400;
+  color: #909399;
+}
 .mc-kr-row {
   border: 1px solid #e4e7ed;
   border-radius: 6px;