feat: add workspace file management and embedded browsing

Users previously had to leave the workbar to manage project files and inspect Git branches or commit history. Add file and directory creation, rename, move, delete and properties, plus searchable branches, branch creation and switching, explicit fetch, and commit file diffs.

Keep file previews in the right workspace pane with directory expansion, selection, scroll and focus preserved on return. Add compact action menus, directory pickers, preview refresh and source switching. Embed the shared browser session directly in the workbar with navigation, resizing and fullscreen controls instead of a separate interaction window.

Moves stay within the current workspace, deletion is permanent after confirmation, and Git switch reports conflicts without discarding or stashing changes. Typecheck, lint and staged whitespace checks pass; existing full-suite failures and the blocked real remote directory validation remain recorded in the workbar progress document.

Release note: 可在右侧工作区管理文件、切换 Git 分支并查看提交历史，返回预览后保留浏览位置；浏览器支持在工作栏内直接交互和全屏显示。

FEATURES.md

@@ -575,9 +575,10 @@ otherwise.
   draft, diagnostic choice, and request ID. Conversations, Prompts,
   credentials, file contents, paths, raw provider responses, and remote Agent
   logs are never attached.
-- [x] **Private-network compatibility mode**: Enabled by default and permits
-  in-app HTTP plus invalid, self-signed, or expired HTTPS certificates.
-  Disabling it restores strict address and certificate validation.
+- [x] **Private-network compatibility**: Permits in-app HTTP plus invalid,
+  self-signed, or expired HTTPS certificates. Fixed platform services such as
+  feedback and WeChat credential or media endpoints retain strict certificate
+  validation.
 
 ### Open source, builds, and releases