Extract SwiftData models to shared ArkavoDataModels package

### Problem
SwiftData models (`Account`, `Profile`, `Stream`, `Thought`, `BlockedProfile`) are currently duplicated/copied between:
- **Arkavo** (iOS app) - located in `Arkavo/Arkavo/`
- **ArkavoCreator** (macOS app) - needs same models
- This violates DRY principle and makes maintenance difficult

### Proposed Solution
Create a new Swift Package: **ArkavoDataModels**

### Package Structure
```
ArkavoDataModels/
├── Package.swift
├── Sources/
│ └── ArkavoDataModels/
│ ├── Models/
│ │ ├── Account.swift
│ │ ├── Profile.swift
│ │ ├── Stream.swift
│ │ ├── Thought.swift
│ │ └── BlockedProfile.swift
│ ├── DTOs/
│ │ ├── ThoughtServiceModel.swift
│ │ └── ProfileDTO.swift
│ ├── Enums/
│ │ ├── MediaType.swift
│ │ ├── Policies.swift
│ │ └── VerificationTypes.swift
│ └── Extensions/
│ └── ModelExtensions.swift
```

### Benefits
- ✅ Single source of truth for data models
- ✅ Shared between iOS and macOS apps
- ✅ Easier testing (isolated package)
- ✅ Better modularity
- ✅ Consistent data layer across platforms

### Migration Steps
1. Create `ArkavoDataModels` package in `app/ArkavoDataModels/`
2. Move model files from `Arkavo/Arkavo/` to package
3. Update `Arkavo.xcodeproj` to depend on package
4. Update `ArkavoCreator.xcodeproj` to depend on package
5. Update imports across both apps
6. Run tests to verify

Start in app/Arkavo/Arkavo/ and inventory the listed model files, then review both Arkavo.xcodeproj and ArkavoCreator.xcodeproj to understand their current model references. Create the package under app/ArkavoDataModels/ with the proposed structure, update both project dependencies and imports, and run the existing tests to verify both apps use the shared models.

Written by the indexing model from the issue text.