fix: resolve Octane Docker build failure on Alpine

[ibourgeois]

Context

As a Laravel developer installing Beacon into an application, I need the generated Octane Dockerfile to build successfully on a clean Alpine-based image so the composer run beacon:build workflow works out of the box.

Acceptance Criteria

• reproduce the current Docker build failure from a Beacon-generated Octane Dockerfile in a Laravel application
• update the generated Octane Dockerfile so pecl install swoole does not fail on Alpine due to missing Brotli build requirements
• ensure the fix works with the current Beacon PHP 8.4 Alpine runtime baseline
• add automated coverage for the Dockerfile output or build path so this regression is caught in package development
• document any required tradeoff if Beacon disables an optional Swoole feature instead of installing extra system packages

Notes

Observed from a real package install in a test Laravel application:

• composer run beacon:build failed during the generated Docker build
• the failure occurs while installing Swoole in the Octane image on php:8.4-cli-alpine
• configure: error: Package requirements (libbrotlienc) were not met
• current generated Dockerfile runs pecl install swoole without adding the Brotli development package or disabling Brotli support