feat(core): implement git worktree checkpoint system

Add comprehensive worktree management system to enable task isolation and rollback capabilities. This allows users to revert agent changes if they don't satisfy requirements or break functionality.

Key components:
- New WorktreeManager service for branch and worktree operations
- GitDiffPanel component for visualizing changes
- Enhanced UI components with worktree integration
- Auto-mode service enhancements for worktree workflow

Modified files: worktree-manager.js, git-diff-panel.tsx, main.js, preload.js, feature-loader.js, agent-output-modal.tsx, board-view.tsx, kanban-card.tsx, electron.ts, app-store.ts, electron.d.ts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

app/electron/main.js

@@ -803,3 +803,134 @@ ipcMain.handle("openai:test-connection", async (_, { apiKey }) => {
     return { success: false, error: error.message };
   }
 });
+
+// ============================================================================
+// Worktree Management IPC Handlers
+// ============================================================================
+
+/**
+ * Revert feature changes by removing the worktree
+ * This effectively discards all changes made by the agent
+ */
+ipcMain.handle(
+  "worktree:revert-feature",
+  async (_, { projectPath, featureId }) => {
+    console.log("[IPC] worktree:revert-feature called with:", {
+      projectPath,
+      featureId,
+    });
+    try {
+      const sendToRenderer = (data) => {
+        if (mainWindow && !mainWindow.isDestroyed()) {
+          mainWindow.webContents.send("auto-mode:event", data);
+        }
+      };
+
+      return await autoModeService.revertFeature({
+        projectPath,
+        featureId,
+        sendToRenderer,
+      });
+    } catch (error) {
+      console.error("[IPC] worktree:revert-feature error:", error);
+      return { success: false, error: error.message };
+    }
+  }
+);
+
+/**
+ * Merge feature worktree changes back to main branch
+ */
+ipcMain.handle(
+  "worktree:merge-feature",
+  async (_, { projectPath, featureId, options }) => {
+    console.log("[IPC] worktree:merge-feature called with:", {
+      projectPath,
+      featureId,
+      options,
+    });
+    try {
+      const sendToRenderer = (data) => {
+        if (mainWindow && !mainWindow.isDestroyed()) {
+          mainWindow.webContents.send("auto-mode:event", data);
+        }
+      };
+
+      return await autoModeService.mergeFeature({
+        projectPath,
+        featureId,
+        options,
+        sendToRenderer,
+      });
+    } catch (error) {
+      console.error("[IPC] worktree:merge-feature error:", error);
+      return { success: false, error: error.message };
+    }
+  }
+);
+
+/**
+ * Get worktree info for a feature
+ */
+ipcMain.handle(
+  "worktree:get-info",
+  async (_, { projectPath, featureId }) => {
+    try {
+      return await autoModeService.getWorktreeInfo({ projectPath, featureId });
+    } catch (error) {
+      console.error("[IPC] worktree:get-info error:", error);
+      return { success: false, error: error.message };
+    }
+  }
+);
+
+/**
+ * Get worktree status (changed files, commits)
+ */
+ipcMain.handle(
+  "worktree:get-status",
+  async (_, { projectPath, featureId }) => {
+    try {
+      return await autoModeService.getWorktreeStatus({ projectPath, featureId });
+    } catch (error) {
+      console.error("[IPC] worktree:get-status error:", error);
+      return { success: false, error: error.message };
+    }
+  }
+);
+
+/**
+ * List all feature worktrees
+ */
+ipcMain.handle("worktree:list", async (_, { projectPath }) => {
+  try {
+    return await autoModeService.listWorktrees({ projectPath });
+  } catch (error) {
+    console.error("[IPC] worktree:list error:", error);
+    return { success: false, error: error.message };
+  }
+});
+
+/**
+ * Get file diffs for a worktree
+ */
+ipcMain.handle("worktree:get-diffs", async (_, { projectPath, featureId }) => {
+  try {
+    return await autoModeService.getFileDiffs({ projectPath, featureId });
+  } catch (error) {
+    console.error("[IPC] worktree:get-diffs error:", error);
+    return { success: false, error: error.message };
+  }
+});
+
+/**
+ * Get diff for a specific file in a worktree
+ */
+ipcMain.handle("worktree:get-file-diff", async (_, { projectPath, featureId, filePath }) => {
+  try {
+    return await autoModeService.getFileDiff({ projectPath, featureId, filePath });
+  } catch (error) {
+    console.error("[IPC] worktree:get-file-diff error:", error);
+    return { success: false, error: error.message };
+  }
+});