feat: explorer copy-path & @-reference actions; icons on tabs and + menu

- Tabs, the + menu, and empty-pane cards carry per-type icons (folder /
  branch / terminal / code file); a terminal glyph joins the icon set
- Hovering an explorer row reveals an @文件 button at the far right that
  appends @<relative path> to the composer draft (session-scoped input
  service, space-separated append)
- Right-clicking a row opens a context menu: copy relative / absolute
  path (writeClipboard + transient in-row "copied" label)
- Rows become div role=button (Enter/Space) to host the inner button;
  relativeTo helper unit-tested

src/client/locales.ts

@@ -66,6 +66,9 @@ const zh = {
   newFile: '新文件',
   openEditor: '打开编辑器',
   gitDetail: '查看变更详情',
+  referenceFile: '@文件',
+  copyRelative: '复制相对地址',
+  copyAbsolute: '复制绝对地址',
 }
 
 const en: Record<keyof typeof zh, string> = {
@@ -129,6 +132,9 @@ const en: Record<keyof typeof zh, string> = {
   newFile: 'New file',
   openEditor: 'Open editor',
   gitDetail: 'View change details',
+  referenceFile: '@file',
+  copyRelative: 'Copy relative path',
+  copyAbsolute: 'Copy absolute path',
 }
 
 /** Translate a copy key in the browser's language (zh → zh, else en). */