Add collapsible sidebar sections for pipeline stages

[elasticsounds]

Summary

• Organizes the pipeline sidebar into three visual sections: Core (always visible), Learning Tools (collapsible, persisted to localStorage), and Packaging
• Adds section headers with a collapsible toggle and info tooltip for Learning Tools
• Reorders stages in stage-config.ts to match section groupings and updates tests accordingly
• Adds i18n translations for new strings in all three locales (en, pt-BR, es)

Test plan

• Verify sidebar renders three distinct sections with headers
• Verify Learning Tools section collapses/expands and state persists across page reloads
• Verify navigating to a learning tool stage forces the section open
• Verify info tooltip appears on hover over the Learning Tools info icon