fix: commit & push now saves pending content and refreshes modified files

Root cause: Two problems caused "0 files changed":
1. loadModifiedFiles() was only called on mount, never refreshed after saves
2. Pending editor content wasn't flushed to disk before git commit

Fix:
- useEditorSave: add savePending() to flush unsaved content, onAfterSave
  callback to refresh git status after Cmd+S
- useCommitFlow: new hook managing save→commit→push flow with proper
  sequencing (save pending → refresh files → show dialog → commit)
- App.tsx: wire onAfterSave to loadModifiedFiles, use useCommitFlow
- git.rs: include stdout in error when stderr is empty (fixes "nothing
  to commit" message being swallowed)
- mock-tauri: track saved files so get_modified_files reflects edits

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

src/hooks/useCommitFlow.test.ts

@@ -0,0 +1,75 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+import { renderHook, act } from '@testing-library/react'
+import { useCommitFlow } from './useCommitFlow'
+
+describe('useCommitFlow', () => {
+  let savePending: vi.Mock
+  let loadModifiedFiles: vi.Mock
+  let commitAndPush: vi.Mock
+  let setToastMessage: vi.Mock
+
+  beforeEach(() => {
+    savePending = vi.fn().mockResolvedValue(undefined)
+    loadModifiedFiles = vi.fn().mockResolvedValue(undefined)
+    commitAndPush = vi.fn().mockResolvedValue('Committed and pushed')
+    setToastMessage = vi.fn()
+  })
+
+  function renderCommitFlow() {
+    return renderHook(() => useCommitFlow({ savePending, loadModifiedFiles, commitAndPush, setToastMessage }))
+  }
+
+  it('openCommitDialog saves pending, refreshes files, then opens dialog', async () => {
+    const { result } = renderCommitFlow()
+    expect(result.current.showCommitDialog).toBe(false)
+
+    await act(async () => {
+      await result.current.openCommitDialog()
+    })
+
+    expect(savePending).toHaveBeenCalledTimes(1)
+    expect(loadModifiedFiles).toHaveBeenCalledTimes(1)
+    expect(result.current.showCommitDialog).toBe(true)
+  })
+
+  it('handleCommitPush saves pending, commits, shows toast, and refreshes files', async () => {
+    const { result } = renderCommitFlow()
+
+    await act(async () => {
+      await result.current.handleCommitPush('test message')
+    })
+
+    expect(savePending).toHaveBeenCalled()
+    expect(commitAndPush).toHaveBeenCalledWith('test message')
+    expect(setToastMessage).toHaveBeenCalledWith('Committed and pushed')
+    expect(loadModifiedFiles).toHaveBeenCalled()
+    expect(result.current.showCommitDialog).toBe(false)
+  })
+
+  it('handleCommitPush shows error toast on failure', async () => {
+    commitAndPush.mockRejectedValueOnce(new Error('push failed'))
+    const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
+    const { result } = renderCommitFlow()
+
+    await act(async () => {
+      await result.current.handleCommitPush('test')
+    })
+
+    expect(setToastMessage).toHaveBeenCalledWith(expect.stringContaining('Commit failed'))
+    consoleSpy.mockRestore()
+  })
+
+  it('closeCommitDialog closes the dialog', async () => {
+    const { result } = renderCommitFlow()
+
+    await act(async () => {
+      await result.current.openCommitDialog()
+    })
+    expect(result.current.showCommitDialog).toBe(true)
+
+    act(() => {
+      result.current.closeCommitDialog()
+    })
+    expect(result.current.showCommitDialog).toBe(false)
+  })
+})