refactor: implement ALLOWED_ROOT_DIRECTORY security and fix path validation

This commit consolidates directory security from two environment variables
(WORKSPACE_DIR, ALLOWED_PROJECT_DIRS) into a single ALLOWED_ROOT_DIRECTORY variable
while maintaining backward compatibility.

Changes:
- Re-enabled path validation in security.ts (was previously disabled)
- Implemented isPathAllowed() to check ALLOWED_ROOT_DIRECTORY with DATA_DIR exception
- Added backward compatibility for legacy ALLOWED_PROJECT_DIRS and WORKSPACE_DIR
- Implemented path traversal protection via isPathWithinDirectory() helper
- Added PathNotAllowedError custom exception for security violations
- Updated all FS route endpoints to validate paths and return 403 on violation
- Updated template clone endpoint to validate project paths
- Updated workspace config endpoints to use ALLOWED_ROOT_DIRECTORY
- Fixed stat() response property access bug in project-init.ts
- Updated security tests to expect actual validation behavior

Security improvements:
- Path validation now enforced at all layers (routes, project init, agent services)
- appData directory (DATA_DIR) always allowed for settings/credentials
- Backward compatible with existing ALLOWED_PROJECT_DIRS/WORKSPACE_DIR configurations
- Protection against path traversal attacks

Backend test results: 654/654 passing ✅

🤖 Generated with Claude Code

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

apps/ui/src/components/views/board-view/worktree-panel/components/worktree-tab.tsx

@@ -191,7 +191,9 @@ export function WorktreeTab({
             )}
             onClick={() => onSelectWorktree(worktree)}
             disabled={isActivating}
-            title="Click to preview main"
+            title={`Click to preview ${worktree.branch}`}
+            aria-label={worktree.branch}
+            data-testid={`worktree-branch-${worktree.branch}`}
           >
             {isRunning && <Loader2 className="w-3 h-3 animate-spin" />}
             {isActivating && !isRunning && (

apps/ui/src/components/views/welcome-view.tsx

@@ -239,6 +239,24 @@ export function WelcomeView() {
       const api = getElectronAPI();
       const projectPath = `${parentDir}/${projectName}`;
 
+      // Validate that parent directory exists
+      const parentExists = await api.exists(parentDir);
+      if (!parentExists) {
+        toast.error("Parent directory does not exist", {
+          description: `Cannot create project in non-existent directory: ${parentDir}`,
+        });
+        return;
+      }
+
+      // Verify parent is actually a directory
+      const parentStat = await api.stat(parentDir);
+      if (parentStat && !parentStat.isDirectory) {
+        toast.error("Parent path is not a directory", {
+          description: `${parentDir} is not a directory`,
+        });
+        return;
+      }
+
       // Create project directory
       const mkdirResult = await api.mkdir(projectPath);
       if (!mkdirResult.success) {