[P1] Add Saved Connection Profiles

## Feature Request

**Priority:** P1 (High)

### Description

CosmosDB Shell has no way to save, list, or switch between named connection profiles. Power users managing multiple accounts/environments must re-type connection strings each time.

### Comparable Features in Other Shells

- **sqlcmd**: `sqlcmd config` subcommands (`config view`, `config use-context`)

### Proposed Behavior

Add a `profile` or `config` command:
- `profile save ` — Save current connection as a named profile
- `profile list` — List saved profiles
- `profile use ` — Connect using a saved profile
- `profile delete ` — Remove a saved profile
- Store profiles securely (credential store integration or encrypted file)

### Example Usage

```
connect --connect "AccountEndpoint=..." --connect-mode direct
profile save prod-account

profile list
profile use dev-account
```

先查看现有的 connect 命令和 shell 的命令处理入口，然后比较 profile save、list、use 和 delete 的建议流程。在实现之前，确定安全的凭据存储应如何工作。完成的标准是：能够保存、列出、选择和删除命名 profile，而无需重新输入连接字符串。

由索引模型根据 Issue 内容生成。