fix: 修复 @ typeahead 文件搜索无结果的问题

execa 新版将 signal 选项重命名为 cancelSignal，导致 execFileNoThrowWithCwd
调用 git ls-files 时抛出 TypeError，文件索引始终为空。同时改进了
FileIndex 的模糊匹配算法，从多个词边界起始位置评分取最优，提升搜索排名质量。

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/hooks/fileSuggestions.ts

@@ -253,15 +253,14 @@ async function getFilesUsingGit(
   logForDebugging(`[FileIndex] getFilesUsingGit called`)
 
   // Check if we're in a git repo. findGitRoot is LRU-memoized per path.
-  const repoRoot = findGitRoot(getCwd())
+  const cwd = getCwd()
+  const repoRoot = findGitRoot(cwd)
   if (!repoRoot) {
     logForDebugging(`[FileIndex] not a git repo, returning null`)
     return null
   }
 
   try {
-    const cwd = getCwd()
-
     // Get tracked files (fast - reads from git index)
     // Run from repoRoot so paths are relative to repo root, not CWD
     const lsFilesStart = Date.now()
@@ -634,7 +633,9 @@ function findMatchingFiles(
  */
 const REFRESH_THROTTLE_MS = 5_000
 export function startBackgroundCacheRefresh(): void {
-  if (fileListRefreshPromise) return
+  if (fileListRefreshPromise) {
+    return
+  }
 
   // Throttle only when a cache exists — cold start must always populate.
   // Refresh immediately when .git/index mtime changed (tracked files).