fix: normalize "bedrock" provider ID to "amazon-bedrock"

Add "bedrock" and "aws-bedrock" as aliases for the canonical
"amazon-bedrock" provider ID in normalizeProviderId().

Without this mapping, configuring a model as "bedrock/..." causes
the auth resolution fallback to miss the Bedrock-specific AWS SDK
path, since the fallback check requires normalized === "amazon-bedrock".
This primarily affects the main agent when the explicit auth override
is not preserved through config merging.

Fixes #15716

src/agents/model-selection.ts

@@ -50,6 +50,9 @@ export function normalizeProviderId(provider: string): string {
   if (normalized === "kimi-code") {
     return "kimi-coding";
   }
+  if (normalized === "bedrock" || normalized === "aws-bedrock") {
+    return "amazon-bedrock";
+  }
   // Backward compatibility for older provider naming.
   if (normalized === "bytedance" || normalized === "doubao") {
     return "volcengine";