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/coding-agent/src/cli/args.ts

@@ -243,6 +243,11 @@ ${chalk.bold("Environment Variables:")}
   XAI_API_KEY             - xAI Grok API key
   OPENROUTER_API_KEY      - OpenRouter API key
   ZAI_API_KEY             - ZAI API key
+  AWS_PROFILE             - AWS profile for Amazon Bedrock
+  AWS_ACCESS_KEY_ID       - AWS access key for Amazon Bedrock
+  AWS_SECRET_ACCESS_KEY   - AWS secret key for Amazon Bedrock
+  AWS_BEARER_TOKEN_BEDROCK - Bedrock API key (bearer token)
+  AWS_REGION              - AWS region for Amazon Bedrock (e.g., us-east-1)
   ${ENV_AGENT_DIR.padEnd(23)} - Session storage directory (default: ~/${CONFIG_DIR_NAME}/agent)
 
 ${chalk.bold("Available Tools (default: read, bash, edit, write):")}

packages/coding-agent/src/cli/list-models.ts

@@ -25,7 +25,7 @@ function formatTokenCount(count: number): string {
  * List available models, optionally filtered by search pattern
  */
 export async function listModels(modelRegistry: ModelRegistry, searchPattern?: string): Promise<void> {
-	const models = await modelRegistry.getAvailable();
+	const models = modelRegistry.getAvailable();
 
 	if (models.length === 0) {
 		console.log("No models available. Set API keys in environment variables.");