feat(ai): Add Amazon Bedrock provider (#494)

Adds support for Amazon Bedrock with Claude models including:
- Full streaming support via Converse API
- Reasoning/thinking support for Claude models
- Cross-region inference model ID handling
- Multiple AWS credential sources (profile, IAM keys, API keys)
- Image support in messages and tool results
- Unicode surrogate sanitization

Also adds 'Adding a New Provider' documentation to AGENTS.md and README.

Co-authored-by: nickchan2 <nickchan2@users.noreply.github.com>

packages/ai/test/bedrock-utils.ts

@@ -0,0 +1,18 @@
+/**
+ * Utility functions for Amazon Bedrock tests
+ */
+
+/**
+ * Check if any valid AWS credentials are configured for Bedrock.
+ * Returns true if any of the following are set:
+ * - AWS_PROFILE (named profile from ~/.aws/credentials)
+ * - AWS_ACCESS_KEY_ID + AWS_SECRET_ACCESS_KEY (IAM keys)
+ * - AWS_BEARER_TOKEN_BEDROCK (Bedrock API key)
+ */
+export function hasBedrockCredentials(): boolean {
+	return !!(
+		process.env.AWS_PROFILE ||
+		(process.env.AWS_ACCESS_KEY_ID && process.env.AWS_SECRET_ACCESS_KEY) ||
+		process.env.AWS_BEARER_TOKEN_BEDROCK
+	);
+}