feat: light theme with runtime Light/Dark toggle - #11

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Function '<arrow>' exceeds both complexity thresholds: • Severity: high • Cyclomatic: 30 (threshold: 20) • Cognitive: 39 (threshold: 15) • Lines: 160 Consider splitting this function into smaller, focused functions.

Function 'RealtimeChart' is hard to understand (cognitive: 27, threshold: 15). • Severity: high • Cyclomatic: 6 • Cognitive: 27 • Lines: 347 High cognitive complexity means deeply nested or interleaved logic. Consider flattening control flow or extracting helper functions.

Function 'Home' exceeds both complexity thresholds: • Severity: critical • Cyclomatic: 34 (threshold: 20) • Cognitive: 102 (threshold: 15) • Lines: 586 Consider splitting this function into smaller, focused functions.

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Fallow: Gate outcomes: passed audit-verdict.