feat(git): add diff, branch, checkout, push, pull to Git sidebar panel

Extends GitOperations.js with diff/branches/checkoutBranch/push/pull,
wires the 5 new IPC handlers in main.js (reusing the existing dir
resolution), whitelists the new channels in preload.js, and fixes the
Git sidebar panel's previously dead _gitDiff callback by wiring up a
diff view, branch list/create/checkout UI, and push/pull buttons.
Resolves Task 5, which deferred this work to this task.

Amit Haridas

tests/main/GitOperations.test.js

@@ -0,0 +1,102 @@
+const fs = require('fs');
+const os = require('os');
+const path = require('path');
+const simpleGit = require('simple-git');
+const GitOperations = require('../../src/main/GitOperations');
+
+describe('GitOperations', () => {
+  let tmpDir, filePath;
+
+  beforeEach(async () => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'gitops_'));
+    const git = simpleGit(tmpDir);
+    await git.init();
+    await git.addConfig('user.name', 'Test User');
+    await git.addConfig('user.email', 'test@example.com');
+    filePath = path.join(tmpDir, 'file.txt');
+    fs.writeFileSync(filePath, 'line1\n');
+    await git.add(['file.txt']);
+    await git.commit('initial commit');
+  });
+
+  afterEach(() => fs.rmSync(tmpDir, { recursive: true, force: true }));
+
+  describe('diff', () => {
+    test('returns full working-tree diff when no file given', async () => {
+      fs.writeFileSync(filePath, 'line1\nline2\n');
+      const result = await GitOperations.diff(tmpDir);
+      expect(typeof result).toBe('string');
+      expect(result).toContain('file.txt');
+      expect(result).toContain('+line2');
+    });
+
+    test('returns diff scoped to a single file', async () => {
+      fs.writeFileSync(filePath, 'line1\nline2\n');
+      const result = await GitOperations.diff(tmpDir, 'file.txt');
+      expect(typeof result).toBe('string');
+      expect(result).toContain('+line2');
+    });
+
+    test('returns error object for non-git directory', async () => {
+      const nonGitDir = fs.mkdtempSync(path.join(os.tmpdir(), 'notgit_'));
+      const result = await GitOperations.diff(nonGitDir);
+      expect(result).toHaveProperty('error');
+      fs.rmSync(nonGitDir, { recursive: true, force: true });
+    });
+  });
+
+  describe('branches', () => {
+    test('returns local branch summary with current branch set', async () => {
+      const result = await GitOperations.branches(tmpDir);
+      expect(result).toHaveProperty('all');
+      expect(result).toHaveProperty('current');
+      expect(result).toHaveProperty('branches');
+      expect(result.all).toContain(result.current);
+    });
+
+    test('returns error object for non-git directory', async () => {
+      const nonGitDir = fs.mkdtempSync(path.join(os.tmpdir(), 'notgit_'));
+      const result = await GitOperations.branches(nonGitDir);
+      expect(result).toHaveProperty('error');
+      fs.rmSync(nonGitDir, { recursive: true, force: true });
+    });
+  });
+
+  describe('checkoutBranch', () => {
+    test('creates and switches to a new branch when isNew is true', async () => {
+      const result = await GitOperations.checkoutBranch(tmpDir, 'feature-x', true);
+      expect(result).not.toHaveProperty('error');
+      const branchInfo = await GitOperations.branches(tmpDir);
+      expect(branchInfo.current).toBe('feature-x');
+    });
+
+    test('switches to an existing branch when isNew is false', async () => {
+      const initialBranches = await GitOperations.branches(tmpDir);
+      const original = initialBranches.current;
+      await GitOperations.checkoutBranch(tmpDir, 'feature-y', true);
+      const result = await GitOperations.checkoutBranch(tmpDir, original, false);
+      expect(result).not.toHaveProperty('error');
+      const branchInfo = await GitOperations.branches(tmpDir);
+      expect(branchInfo.current).toBe(original);
+    });
+
+    test('returns error object when checking out a nonexistent branch', async () => {
+      const result = await GitOperations.checkoutBranch(tmpDir, 'does-not-exist', false);
+      expect(result).toHaveProperty('error');
+    });
+  });
+
+  describe('push', () => {
+    test('returns error object when no remote is configured', async () => {
+      const result = await GitOperations.push(tmpDir);
+      expect(result).toHaveProperty('error');
+    });
+  });
+
+  describe('pull', () => {
+    test('returns error object when no remote is configured', async () => {
+      const result = await GitOperations.pull(tmpDir);
+      expect(result).toHaveProperty('error');
+    });
+  });
+});