[Feature Request]: Migrate Node Templates to Workflows

## Is there an existing issue for this?

- [x] I have searched the existing issues and checked the recent builds/commits

## What would your feature do ?

This feature would remove the legacy "Node Templates" functionality and integrate it with the modern Workflows system. Currently, Node Templates allows users to save node/group selections as reusable templates (stored as JSON files), but this functionality has become obsolete since the introduction of the "workflow insert" feature.

The proposed changes would:
1. Remove "Node Templates >" from the canvas right-click menu
2. Change "Save Selected as Template" to "Save Selected as Workflow..."
3. Save the selection as a workflow that appears in the workflows sidebar
4. Provide automatic migration for existing template JSON files to workflows

This consolidation would simplify the UI and provide a more consistent user experience by having a single system for saving and reusing node configurations.

## Proposed workflow

1. User selects multiple nodes on the canvas
2. Right-click → "Save Selected as Workflow..."
3. Enter a name for the workflow
4. The selection is saved as a workflow and appears in the Workflows sidebar
5. User can insert it later by:
- Right-clicking the workflow in the sidebar → "Insert"
- ... maybe there should be a better way for user to do this or discover how to do it

For existing users with saved templates:
1. On first launch after the update, detect existing `comfy.templates.json` file
2. Automatically migrate each template to a workflow (optionally in a "Migrated Templates" folder)
3. Notify user of the migration with option to review

## Additional information

**Related Issues:**
This consolidates and builds upon existing feature requests:
- #1801 - Manage node templates in workflow sidebar tab
- #1012 - Add the node templates manager to the sidebar

**Technical Details:**
- Node templates are currently stored in `comfy.templates.json` via the user data API
- Implementation is in `src/extensions/core/nodeTemplates.ts`
- Templates include node data and group node configurations
- The feature supports import/export of template collections

**Benefits:**
- Reduces UI complexity by removing redundant functionality
- Provides better discoverability (workflows sidebar is more visible than buried menu option)
- Leverages existing workflow management features (folders, search, etc.)
- Maintains backward compatibility through automatic migration

**Implementation Notes:**
- Migration should convert existing templates to workflow format
- Templates folder in workflows sidebar should have distinct styling
- Preserve template naming and organization during migration
- Consider adding some default/example templates for new users (as suggested in #1012)

┆Issue is synchronized with this [Notion page](https://www.notion.so/Issue-4056-Feature-Request-Migrate-Node-Templates-to-Workflows-2066d73d3650815eaa59f03e98ceab14) by [Unito](https://www.unito.io)