[WIP] [Project Solar / Phase 1] Main feature branch to add modes support to tokens + components + showcase

[didoo]

📌 Summary

This is the main feature branch for the first part of the work needed to create a working integral flow that connects the design tokens pipeline (updated to support $modes) to the CSS for the HDS components (updated to generate multiple CSS files in input, including themed tokens where needed) to the showcase (updated to support theme switching and the theming of HDS components for the their migration to the Carbon visual language, aka "carbonization")

🛠️ Detailed description

📸 Screenshots

🔗 External links

Jira ticket: HDS-XXX
Figma file: [if it applies]

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👀 Component checklist

• Percy was checked for any visual regression
• A changelog entry was added via Changesets if needed (see templates here)

💬 Please consider using conventional comments when reviewing this PR.

📋 PCI review checklist

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.
• If applicable, I've worked with GRC to document the impact of any changes to security controls.
  Examples of changes to controls include access controls, encryption, logging, etc.
• If applicable, I've worked with GRC to ensure compliance due to a significant change to the in-scope PCI environment.
  Examples include changes to operating systems, ports, protocols, services, cryptography-related components, PII processing code, etc.

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Project	Deployment	Preview	Updated (UTC)
hds-showcase	Ready	Preview	Sep 30, 2025 2:54pm
hds-website	Ready	Preview	Sep 30, 2025 2:54pm