feat: add version-aware AWS CLI guidance to credential error messages

[siwachabhi]

Summary

• Credential error messages (expired, invalid, missing) now include version-aware guidance instead of hardcoded aws login strings
• When AWS CLI is not installed or below v2.32.0 (minimum for aws login), users see install/upgrade instructions with a link to the official docs
• Updates stale aws sso login reference to aws login in the pre-deploy identity flow

Changes

File	What changed
src/cli/external-requirements/versions.ts	Added AWS_CLI_MIN_VERSION (2.32.0) constant
src/cli/external-requirements/checks.ts	Added checkAwsCliVersion(), getAwsLoginGuidance() (cached), and parseAwsCliVersion() — follows existing checkNodeVersion pattern
src/cli/external-requirements/index.ts	Re-exported new symbols
src/cli/aws/account.ts	Replaced 3 hardcoded 'Run: aws login' strings with dynamic await getAwsLoginGuidance()
src/cli/operations/deploy/pre-deploy-identity.ts	Changed 'aws sso login' → 'aws login'

Motivation

Users with older AWS CLI versions (< 2.32.0) see Run: aws login in error messages, but aws login doesn't exist in their version. This leads to confusion — they try the command, it fails, and they don't know why. The new guidance detects the installed CLI version and tells users exactly what to do:

• Not installed: "1. Install AWS CLI (v2.32.0+): [link] 2. Run: aws login"
• Old version: "1. Update AWS CLI from vX.Y.Z to v2.32.0+: [link] 2. Run: aws login"
• Current version: "Run: aws login"

Test plan

• All 112 unit tests in checks.test.ts, versions.test.ts, detect.test.ts, account.test.ts, pre-deploy-identity.test.ts pass
• npx tsc --noEmit passes
• Prettier + ESLint + secretlint pass (pre-commit hooks)
• Manual: run agentcore deploy with expired creds and verify guidance message
• Manual: run with AWS CLI < 2.32.0 and verify upgrade guidance appears

[notgitika]

LGTM