refactor(web): hasApplicableFix 改类型谓词，消除 applyConflictFix 强转

hasApplicableFix 重写为对象入参类型谓词 patch is ApplicablePatch，谓词命中后 applyConflictFix 里 original/replacement 自动收窄为 string，删两处 as string；补收窄单测。

apps/web/lib/review/applyFix.ts

@@ -6,15 +6,25 @@ export type FixOutcome =
   | { status: "not-found"; text: string } // 有补丁但终稿里找不到原文（作者已改稿/漂移）：text 原样
   | { status: "no-patch"; text: string }; // 该冲突无可自动应用的补丁：text 原样
 
+// 已确认可应用的补丁（original/replacement 均为 string）。
+export interface ApplicablePatch {
+  original: string;
+  replacement: string;
+}
+
+// 松散补丁入参：original/replacement 可能缺失/为 null（审稿可局部修复时才带上）。
+interface LoosePatch {
+  original: string | null | undefined;
+  replacement: string | null | undefined;
+}
+
 // 是否带可应用补丁：original 非空 + replacement 为字符串（容许空串=删除）。
-export function hasApplicableFix(
-  original: string | null | undefined,
-  replacement: string | null | undefined,
-): boolean {
+// 类型谓词：命中即把 original/replacement 收窄为 string，调用方无需强转。
+export function hasApplicableFix(patch: LoosePatch): patch is ApplicablePatch {
   return (
-    typeof original === "string" &&
-    original.length > 0 &&
-    typeof replacement === "string"
+    typeof patch.original === "string" &&
+    patch.original.length > 0 &&
+    typeof patch.replacement === "string"
   );
 }
 
@@ -25,18 +35,20 @@ export function applyConflictFix(
   original: string | null | undefined,
   replacement: string | null | undefined,
 ): FixOutcome {
-  if (!hasApplicableFix(original, replacement)) {
+  const patch: LoosePatch = { original, replacement };
+  if (!hasApplicableFix(patch)) {
     return { status: "no-patch", text };
   }
-  // hasApplicableFix 已收窄为 string。
-  const from = original as string;
-  const to = replacement as string;
-  const idx = text.indexOf(from);
+  // 谓词已把 patch 收窄为 ApplicablePatch，original/replacement 皆为 string。
+  const idx = text.indexOf(patch.original);
   if (idx === -1) {
     return { status: "not-found", text };
   }
   return {
     status: "applied",
-    text: text.slice(0, idx) + to + text.slice(idx + from.length),
+    text:
+      text.slice(0, idx) +
+      patch.replacement +
+      text.slice(idx + patch.original.length),
   };
 }