feat: git panel redesign (#535)

* feat(git-panel): add Branches tab, Fetch always visible, inline error banners

- Add dedicated Branches tab (local/remote sections, switch with confirmation, delete branch, create branch)
- Rename History tab to Commits; add change-count badge on Changes tab
- Fetch button always visible when remote exists (not only when both ahead & behind)
- Inline error banner below header for failed push/pull/fetch, with dismiss button
- Server: /api/git/branches now returns localBranches + remoteBranches separately
- Server: add /api/git/delete-branch endpoint (prevents deleting current branch)
- Controller: expose operationError, clearOperationError, deleteBranch, localBranches, remoteBranches
- Constants: add deleteBranch to all ConfirmActionType record maps

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: git log datetime

* feat(git-panel): add staged/unstaged sections and enhanced commit details

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Haile <118998054+blackmammoth@users.noreply.github.com>

package-lock.json

@@ -1909,6 +1909,7 @@
       "cpu": [
         "arm64"
       ],
+      "dev": true,
       "license": "LGPL-3.0-or-later",
       "optional": true,
       "os": [
@@ -1925,6 +1926,7 @@
       "cpu": [
         "x64"
       ],
+      "dev": true,
       "license": "LGPL-3.0-or-later",
       "optional": true,
       "os": [