feat: add Gen 1 maintenance mode deprecation warning

[Simone319]

What

Adds a non-suppressible deprecation warning to the Amplify Gen 1 CLI that is printed on every invocation.

Why

AWS Amplify Gen 1 enters maintenance mode on May 1, 2026 and reaches end of life on May 1, 2027. During maintenance mode only critical bug fixes and security patches will be provided. Users must be proactively notified to migrate to Gen 2.

Details

• Warning is printed to stderr (not stdout) so it does not interfere with JSON output, piped commands, or scripted automation that parses stdout.
• Output uses ANSI yellow (\x1b[33m) for visual emphasis, with a reset (\x1b[0m) at the end.
• Runs unconditionally at the top of run() (before deleteOldVersion()). It cannot be suppressed or silenced.
• Includes a direct link to the Gen 2 migration guide.

Warning text

⚠️  WARNING: AWS Amplify Gen 1 CLI is in maintenance mode and will reach end of life on May 1, 2027.
During maintenance mode, only critical bug fixes and security patches will be provided.
Migrate to Amplify Gen 2: https://docs.amplify.aws/react/start/migrate-to-gen2/

Testing

node packages/amplify-cli/bin/amplify version
# Warning appears on stderr before normal output

Checklist

• Change is scoped to a single file (packages/amplify-cli/src/index.ts)
• No new dependencies
• Warning uses stderr to avoid breaking automation
• Migration link included