Issue #, if available: n/a

Summary

• AWS region auto-detection -- Replaced the hardcoded REGION = "us-west-2" in config.ts with a resolveRegion() function that follows the standard AWS precedence chain: AWS_REGION env var → AWS_DEFAULT_REGION env var → ~/.aws/config [default] profile → us-west-2 fallback.

• Startup config warnings -- Added a ConfigWarnings toast system that validates AWS configuration on app launch. Performs an async STS GetCallerIdentity check to catch expired/invalid credentials and alerts when the region falls back to the default. Toasts are styled with the shared glass-morphism pattern and auto-dismiss (12s for warnings, 20s for errors).

• Fixed broken credential error handling -- s3Helper.ts and smHelper.ts had e instanceof CredsExpiredAlert in their catch blocks, but CredsExpiredAlert is a React component, not an Error class. The instanceof check itself threw TypeError: Function has non-object prototype 'undefined', turning every caught AWS error into an uncaught exception. Replaced with a shared isCredentialError() utility that detects auth failures by error name and HTTP status code.

• Fixed S3 client stale credentials -- The S3Client in s3Helper.ts was instantiated once at module load with static credentials. After refreshing ~/.aws/credentials, the client still used the original stale creds. Changed to a credentials provider function so the SDK reads fresh credentials on every request.

• Hardened modal error handling -- Wrapped all async data-fetching useEffect calls in ImageRequestModal, LoadDataModal, and LoadImageModal with try/catch. Fixed res !== undefined null checks (truthy for null) to res && Array.isArray(res) && res.length > 0 to prevent null.map() crashes.

• Modernized CredsExpiredAlert -- Rewrote to use the shared ConfigWarnings.css toast classes instead of inline styles. Added slide-in/out animations, a close (X) button, disabled state during retry, and properly typed props.

• README overhaul -- Rewrote with features overview, architecture table, usage guides, project structure, configuration reference (including region auto-detection docs), and updated resource links. Removed outdated CloudScape reference.

Files changed

Checklist

Before you submit a pull request, please make sure you have the following:

• Code changes are compact and well-structured to facilitate easy review
• Changes are documented in the README.md and other relevant documentation pages
• PR title and description accurately reflect the changes and are detailed enough for historical tracking
• PR contains tests that cover all new code and the code has been manual tested
• All new dependencies are declared (if any), and no unnecessary libraries are added
• Performance impacts (if any) of the changes are evaluated and documented
• Security implications of the changes (if any) are reviewed and addressed
• I have read the Contributing Guidelines and agree to follow the Code of Conduct

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.