🛠️ chore(ratio-sync): improve upstream ratio comparison & output cleanliness

Summary
1. Consider “both unset” as identical
   • When both localValue and upstreamValue are nil, mark upstreamValue as "same" to avoid showing “Not set”.

2. Exclude fully-synced upstream channels from result
   • Scan `differences` to detect channels that contain at least one divergent value.
   • Remove channels whose every ratio is either `"same"` or `nil`, so the frontend only receives actionable discrepancies.

Why
These changes reduce visual noise in the Upstream Ratio Sync table, making it easier for admins to focus on models requiring attention. No functional regressions or breaking API changes are introduced.

web/src/i18n/locales/en.json

@@ -1665,5 +1665,27 @@
   "确定清除所有失效兑换码？": "Are you sure you want to clear all invalid redemption codes?",
   "将删除已使用、已禁用及过期的兑换码，此操作不可撤销。": "This will delete all used, disabled, and expired redemption codes, this operation cannot be undone.",
   "选择过期时间（可选，留空为永久）": "Select expiration time (optional, leave blank for permanent)",
-  "请输入备注（仅管理员可见）": "Please enter a remark (only visible to administrators)"
+  "请输入备注（仅管理员可见）": "Please enter a remark (only visible to administrators)",
+  "上游倍率同步": "Upstream ratio synchronization",
+  "获取渠道失败：": "Failed to get channels: ",
+  "请至少选择一个渠道": "Please select at least one channel",
+  "获取倍率失败：": "Failed to get ratios: ",
+  "后端请求失败": "Backend request failed",
+  "部分渠道测试失败：": "Some channels failed to test: ",
+  "已与上游倍率完全一致，无需同步": "The upstream ratio is completely consistent, no synchronization is required",
+  "请求后端接口失败：": "Failed to request the backend interface: ",
+  "同步成功": "Synchronization successful",
+  "部分保存失败": "Some settings failed to save",
+  "保存失败": "Save failed",
+  "选择同步渠道": "Select synchronization channel",
+  "应用同步": "Apply synchronization",
+  "倍率类型": "Ratio type",
+  "当前值": "Current value",
+  "上游值": "Upstream value",
+  "差异": "Difference",
+  "搜索渠道名称或地址": "Search channel name or address",
+  "缓存倍率": "Cache ratio",
+  "暂无差异化倍率显示": "No differential ratio display",
+  "请先选择同步渠道": "Please select the synchronization channel first",
+  "与本地相同": "Same as local"
 }