* fix: propagate AWS SDK auth sentinel for IMDS/instance role Bedrock auth
When Bedrock auth resolves via AWS SDK default credential chain (IMDS,
ECS task role) with no explicit API key, the auth controller returned
early without calling setRuntimeApiKey(). This left pi's authStorage
unaware that the provider is authenticated, causing 'No API key found
for amazon-bedrock' errors.
Now, when mode is 'aws-sdk' and no explicit API key is available:
1. Try prepareProviderRuntimeAuth to resolve runtime credentials
2. If that returns a real apiKey, use it with auth refresh scheduling
3. Otherwise inject a '__aws_sdk_auth__' sentinel so pi's
hasConfiguredAuth() passes and the AWS SDK handles request signing
This is a focused fix in auth-controller.ts only, avoiding the risky
model-auth-runtime-shared.ts changes that could re-introduce the
fake-apiKey injection pattern on ECS (see prior regressions #49891,
#50699, #54274).
Fixes#62995
* fix(pi-auth): clean up aws-sdk sentinel fallback
* docs(changelog): note aws-sdk Bedrock auth fix
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Co-authored-by: Vincent Koc <vincentkoc@ieee.org>
c7e5289fd2