refactor: convert all LeetCode solutions to Go-only

Changes:
- Removed all Java code implementations
- Kept only Go language solutions
- Renamed "## Go 解法" to "## 解法"
- Removed "### Go 代码要点" sections
- Cleaned up duplicate headers and empty sections
- Streamlined documentation for better readability

Updated files (9):
- 三数之和.md
- 两数相加.md
- 无重复字符的最长子串.md
- 最长回文子串.md
- 括号生成.md
- 子集.md
- 单词搜索.md
- 电话号码的字母组合.md
- 柱状图中最大的矩形.md

All 22 LeetCode Hot 100 Medium problems now use Go exclusively.
Code is cleaner, more focused, and easier to follow.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

16-LeetCode Hot 100/无重复字符的最长子串.md

@@ -46,7 +46,7 @@ LeetCode 3. Medium
 
 ---
 
-## Go 解法
+## 解法
 
 ```go
 func lengthOfLongestSubstring(s string) int {
@@ -74,16 +74,8 @@ func lengthOfLongestSubstring(s string) int {
 }
 ```
 
-### Go 代码要点
-1. 使用 `range` 遍历字符串，自动处理 Unicode
-2. `map[rune]int` 记录字符索引
-3. 条件判断：`idx >= left` 确保在窗口内
-
 ---
 
-## 解法
-
-
 ---
 
 ## 图解过程