feat(migration-bundle): Add preset management for migration configurations

[mariusorani]

Summary

This PR adds preset management capabilities to the Migration Bundle extension, allowing users to save and load migration configurations using Directus native presets/bookmarks system.

Problem

Currently, users need to re-enter migration details (URL, token, options) every time they use the migration tool. This leads to:

• Repetitive manual input for frequent migrations
• Risk of errors from incorrect URLs or tokens
• No way to share configurations between team members
• Difficulty in maintaining consistent migration setups

Solution

This PR implements a comprehensive preset management system:

1. Environment Variable Defaults

MIGRATION_BUNDLE_DEFAULT_URL=https://staging.example.com
MIGRATION_BUNDLE_DEFAULT_TOKEN=your-admin-token
MIGRATION_BUNDLE_DEFAULT_OPTIONS=content,users,flows

2. User Presets/Bookmarks

- Save current configuration as a named preset
- Load saved presets from dropdown
- Update existing presets when changes are made
- Delete presets no longer needed

3. Modern UI/UX

- Integrated preset selector with bookmark icon
- Visual feedback when preset has unsaved changes
- Smooth animations for update button
- Clean, modern design matching Directus UI

Changes

Backend (migration-endpoint/index.ts)

- ✨ Added /defaults endpoint for ENV-based configuration
- ✨ Added /presets GET endpoint to fetch user presets
- ✨ Added /presets POST endpoint to create/update presets
- ✨ Added /presets/:id DELETE endpoint to remove presets
- 🔒 Proper permission checks (admin only)
- 💾 Presets stored in directus_presets table

Frontend (module.vue)

- ✨ Preset selector dropdown with "Load from Environment Defaults" option
- ✨ Save button to create new presets (bookmark icon)
- ✨ Update button appears when preset has changes
- ✨ Visual indicators for unsaved changes
- 🗑️ Removed localStorage implementation completely
- 🎨 Modern UI with smooth transitions

Types (extension.ts)

- 🏷️ Added MigrationConfig interface
- 🏷️ Updated type definitions

Screenshots

[Add screenshots showing:
1. Preset selector dropdown
2. Save preset dialog
3. Update button when changes detected
4. ENV defaults loaded]

Testing

1. Test ENV defaults:
# Set in .env
MIGRATION_BUNDLE_DEFAULT_URL=https://test.com
MIGRATION_BUNDLE_DEFAULT_TOKEN=test-token
MIGRATION_BUNDLE_DEFAULT_OPTIONS=content,users
  - Navigate to /admin/migration
  - Verify defaults are loaded
2. Test preset creation:
  - Fill in migration details
  - Click bookmark button
  - Save with name "Production Config"
  - Verify preset appears in dropdown
3. Test preset loading:
  - Select different presets from dropdown
  - Verify configuration updates
4. Test preset updates:
  - Load a preset
  - Change some values
  - Verify update button appears
  - Click update and verify changes are saved
5. Test preset deletion:
  - Create test preset
  - Delete it
  - Verify it's removed from dropdown

Breaking Changes

None. This is fully backward compatible.

Migration

No database migrations required - uses existing directus_presets table.