🤖 feat: Add support for Amazon Bedrock

Add Amazon Bedrock as a supported AI provider using @ai-sdk/amazon-bedrock
with flexible AWS authentication via @aws-sdk/credential-providers.

## Authentication Methods

Uses AWS credential provider chain, supporting:
- Environment variables (AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY)
- Shared credentials file (~/.aws/credentials)
- EC2 instance profiles
- ECS task roles
- EKS service accounts (IRSA)
- SSO credentials
- And more...

Or explicit credentials in providers.jsonc:
```json
{
  "bedrock": {
    "region": "us-east-1",
    "accessKeyId": "...",
    "secretAccessKey": "..."
  }
}
```

## Supported Models

Includes Claude, Amazon Nova, Meta Llama, Mistral, and other Bedrock models.

Model string format: bedrock:<model-id>
Example: bedrock:anthropic.claude-3-5-sonnet-20241022-v2:0

Closes #764

Author: ibetitsmike