chore: add design system token layer and migrate hardcoded values

[eskp]

Summary

• Establish a three-layer token architecture so all UI code references semantic CSS variables instead of raw hex/rgb values, preventing visual drift and making theme changes propagate automatically
• Adds a CI-ready audit script (scripts/token-audit.js) that scans for hardcoded visual values, suggests the correct token, and exits non-zero on errors -- 98 errors resolved to reach zero across 18 files
• Centralizes the project/tag color palette into a shared module to eliminate three duplicate arrays

Test plan

• Run node scripts/token-audit.js -- should report 0 errors (74 warnings expected)
• Hub pages render correctly: protocol cards, detail view, strip, minimap all use correct colors
• Template badges show correct blue styling in both light and dark mode
• Project and tag color pickers still function with the shared palette
• SVG connection dots and animated borders render correctly
• Project dot fallback color (when no color assigned) renders as muted text color
• pnpm build succeeds with no type errors

[github-actions]

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Environment Details:

• 🌐 URL: https://app-pr-485.keeperhub.com
• 📦 Namespace: pr-485
• 🏷️ Image Tag: 458c629
• 🔢 Commit: 458c629779cba1d9471d28151783e3c2771ef702

Components:

• Keeperhub Application
• PostgreSQL Database (isolated instance)
• LocalStack (SQS emulation)
• Redis (isolated instance)
• Scheduler Dispatcher (staging image)
• Scheduler Executor (staging image)
• SC Event Tracker (staging image)
• SC Event Worker (staging image)

The environment will be automatically cleaned up when this PR is closed or merged.