feat: save last used project (#778)

### TL;DR

Update the task directory handling to persist the last used directory when changed in the TaskInput component.

### What changed?

- Added a new `setLastUsedDirectory` function to the `taskDirectoryStore`
- Updated the `TaskInput` component to call `setLastUsedDirectory` when a directory is selected
- This ensures the last used directory is properly saved when changed through the UI

### How to test?

1. Open the application and create a new task
2. Select a directory for the task
3. Create another new task
4. Verify that the previously selected directory is pre-selected

### Why make this change?

Previously, when a user selected a directory in the TaskInput component, the selection wasn't being saved to the store's `lastUsedDirectory` state. This change improves the user experience by remembering their last directory choice, making it faster to create multiple tasks in the same directory.

Author: k11kirky

apps/twig/src/renderer/features/task-detail/components/TaskInput.tsx

@@ -70,7 +70,7 @@ export function TaskInput() {
 
   const handleDirectoryChange = (newPath: string) => {
     setSelectedDirectory(newPath);
-    setLastUsedDirectory(newPath);
+    setLastUsedDirectory(newPath || null);
   };
 
   const effectiveWorkspaceMode = workspaceMode;

apps/twig/src/renderer/stores/taskDirectoryStore.ts

@@ -10,7 +10,7 @@ interface TaskDirectoryState {
   lastUsedDirectory: string | null;
   getTaskDirectory: (taskId: string, repoKey?: string) => string | null;
   setRepoDirectory: (repoKey: string, directory: string) => void;
-  setLastUsedDirectory: (directory: string) => void;
+  setLastUsedDirectory: (directory: string | null) => void;
   clearRepoDirectory: (repoKey: string) => void;
   validateLastUsedDirectory: () => Promise<void>;
 }
@@ -52,7 +52,7 @@ export const useTaskDirectoryStore = create<TaskDirectoryState>()(
         }));
       },
 
-      setLastUsedDirectory: (directory: string) => {
+      setLastUsedDirectory: (directory: string | null) => {
         set({ lastUsedDirectory: directory });
       },