chore: 移除 Cursor.ts 中未引用的 kill ring 访问器

- 删除 getKillRingItem、getKillRingSize、clearKillRing、canYankPop（全仓零引用的独立 export）
- 移除 VIM_WORD_CHAR_REGEX 的 export 关键字（仍由 isVimWordChar 内部使用，保留常量本体）

kill ring 特性本身仍活跃（getLastKill/pushToKillRing/yankPop 在 useSearchInput/useTextInput 使用），仅这几个孤儿 helper 未接入。

Co-Authored-By: glm-5.2 <zai-org@claude-code-best.win>

src/utils/Cursor.ts

@@ -51,26 +51,6 @@ export function getLastKill(): string {
   return killRing[0] ?? ''
 }
 
-export function getKillRingItem(index: number): string {
-  if (killRing.length === 0) return ''
-  const normalizedIndex =
-    ((index % killRing.length) + killRing.length) % killRing.length
-  return killRing[normalizedIndex] ?? ''
-}
-
-export function getKillRingSize(): number {
-  return killRing.length
-}
-
-export function clearKillRing(): void {
-  killRing = []
-  killRingIndex = 0
-  lastActionWasKill = false
-  lastActionWasYank = false
-  lastYankStart = 0
-  lastYankLength = 0
-}
-
 export function resetKillAccumulation(): void {
   lastActionWasKill = false
 }
@@ -83,10 +63,6 @@ export function recordYank(start: number, length: number): void {
   killRingIndex = 0
 }
 
-export function canYankPop(): boolean {
-  return lastActionWasYank && killRing.length > 1
-}
-
 export function yankPop(): {
   text: string
   start: number
@@ -130,7 +106,7 @@ export function resetYankState(): void {
  */
 
 // Pre-compiled regex patterns for Vim word detection (avoid creating in hot loops)
-export const VIM_WORD_CHAR_REGEX = /^[\p{L}\p{N}\p{M}_]$/u
+const VIM_WORD_CHAR_REGEX = /^[\p{L}\p{N}\p{M}_]$/u
 export const WHITESPACE_REGEX = /\s/
 
 // Exported helper functions for Vim character classification