fix(theme): correctly normalize paths ending with "index"

src/shared/shared.ts

@@ -17,7 +17,8 @@ export type {
 export const EXTERNAL_URL_RE = /^(?:[a-z]+:|\/\/)/i
 export const APPEARANCE_KEY = 'vitepress-theme-appearance'
 export const HASH_RE = /#.*$/
-export const EXT_RE = /(index)?\.(md|html)$/
+export const EXT_RE = /\.(md|html)$/
+export const INDEX_RE = /\/index$/
 
 export const inBrowser = typeof document !== 'undefined'
 
@@ -61,7 +62,7 @@ export function isActive(
 }
 
 export function normalize(path: string): string {
-  return decodeURI(path).replace(HASH_RE, '').replace(EXT_RE, '')
+  return decodeURI(path).replace(HASH_RE, '').replace(EXT_RE, '').replace(INDEX_RE, '/')
 }
 
 export function isExternal(path: string): boolean {