fix(#141): strip leading './' from coverage-check paths

Non-git tools (e.g. `find`, `ls`) can emit paths with a "./" prefix.
Without stripping this, "./cmd/foo.go" would not match the glob "cmd/**",
producing a false-positive uncovered-file failure.

Fix: add strings.TrimPrefix(f, "./") after backslash normalization.

Test: TestRunValidateDocmap_DotSlashPrefix

Addresses MINOR finding in review #4175.

cmd/review-bot/validatedocmap.go

@@ -178,6 +178,9 @@ func runValidateDocmap(args []string) int {
 		// Normalize Windows-style backslashes to forward slashes so that
 		// changed-file paths from git on Windows match doc-map globs.
 		f = strings.ReplaceAll(f, "\\", "/")
+		// Strip a leading "./" emitted by non-git tools (e.g. `find`) so that
+		// paths like "./cmd/foo.go" match doc-map globs written as "cmd/**".
+		f = strings.TrimPrefix(f, "./")
 		if !review.FileCoveredByDocMap(cfg, f) {
 			uncovered = append(uncovered, f)
 		}