feat: 增加全宽列表视图功能 (#1079)

* feat(mailbox): add list view mode

- Add a toggleable list view for the mailbox, with a settings option and back button.
- deselect mail on second click in list view
- set current mail on row click in multi-action mode

* feat(mailbox): add configurable body preview line clamp

Allow users to set the number of preview lines (0–5) for mail body in the list view via a slider in Appearance settings. Includes i18n support for the new option and its "Off" state.

* chore: clarify some i18n message in settings

include the following changes:
- The original "Mailbox Split Size" to "Left list width in two-column mailbox view"
- The description of new feature "Full-width mailbox list view"
sync all languages with the updated message

* docs: update changelog with recent UI improvements

- Added mailbox full-width list view and body preview lines settings
- Extended left panel width ratio range to 0
- Included English changelog translations

* docs: fix CHANGELOG improvements types

* fix: enable mail list preview line clamp settings on mobile

CHANGELOG.md

@@ -10,6 +10,9 @@
 
 ### Features
 
+- feat: |Frontend| 邮箱新增「邮箱全宽列表视图」开关（在外观设置中控制），开启后默认全宽列表展示邮件标题与正文预览，点击单封邮件再展开为双栏，再次点击同一封邮件可回到列表视图；多选模式下点击邮件会同步切换勾选状态与右侧预览，并禁用同邮件点击收回列表，展开时双栏左侧列表宽度仍遵循「邮箱双栏视图左侧列表宽度占比」配置；默认关闭，保留原有双栏行为
+- feat: |Frontend| 邮箱全宽列表视图新增「正文预览行数」配置（在外观设置中控制），可设置邮件正文预览的最大行数，默认 2 行，0 表示关闭预览
+
 ### Bug Fixes
 
 - fix: |AI 提取| 强化提示词，要求 AI 保持邮件原始链接域名，避免小模型改写验证链接域名导致错误跳转（issue #1072）
@@ -18,6 +21,8 @@
 
 ### Improvements
 
+- feat: |Frontend| 「邮箱双栏视图左侧列表宽度占比」最小值由 0.25 放宽至 0，左侧列表可完全折叠使正文近乎全屏，刻度增加 0 点；收件箱与发件箱的双栏拆分同步生效，并优化外观设置文案以明确该比例控制左侧邮件列表宽度
+
 ## v1.9.0
 
 ### Features