[FEAT] Organize Workflow Definitions into Folders

## Feature Request

### Problem Overview
Once you create many workflow definitions in Studio, it becomes a bit of a chore to see which workflows go with what business process or project without introducing some prefixed naming convention on the workflow name to "sort of" organize the definitions.

### Proposed Solution
Introduce the concept of "Folders" to organize the definition of workflows into containers that help group similar workflows together. This folder structure could be on the Studio sidebar as a sub-menu under the Workflows > Definitions menu:

```yaml
Definitions (existing sidebar menu item)
├── ProjectA
│ ├── MyWorkflowForA1
│ └── MyWorkflowForA2
├── ProjectB
│ ├── MyWorkflowForB1
│ └── MyWorkflowForB2
└── Marketing
└── Newsletter Campaign: March 2024 Edition Workflow
```
**Some ideas:**
- Clicking Definitions takes you to the non-filtered view (same as today).
- Clicking on any of the sub-folders takes you to a filtered view showing only the workflows contained in that folder
- Folders can be added in the sidebar
- Folders can be renamed/deleted/reordered
- Deleting a folder deleted all child workflows (recursively)

### Use Cases
- Organize workflows into folders along business group/department lines
- Organize workflows by the project they relate to

The issue names no files or tests. Start by locating the Studio Workflows > Definitions view and the workflow-definition management entry points; then clarify how folders are stored and managed. Done means folders support adding, renaming, deleting, reordering, filtering, and recursive deletion of child workflows as described.

Written by the indexing model from the issue text.