Define Deployment DTOs (pydantic request/response models)

## Overview

Define pydantic-based request/response models for Deployment REST API.

## Tasks

1. Create DTOs in `src/ai/backend/common/dto/manager/deployment/`:
- DeploymentCreateRequest, DeploymentCreateResponse
- DeploymentUpdateRequest, DeploymentUpdateResponse
- DeploymentListRequest, DeploymentListResponse
- DeploymentDetailResponse
1. Create Revision DTOs:
- RevisionCreateRequest, RevisionCreateResponse
- RevisionListResponse, RevisionDetailResponse
- PromoteRevisionRequest, RollbackRequest
1. Create Policy DTOs:
- DeploymentPolicyUpdateRequest
- AutoScalingPolicyRequest, AutoScalingPolicyResponse
1. Follow existing patterns in `src/ai/backend/common/dto/manager/`

## Reference

- Existing DTOs: src/ai/backend/common/dto/manager/

JIRA Issue: BA-3430