Add kanagawa-wave-blur-theme

[funsaized]

Summary

• Adds Kanagawa Wave Blur theme extension featuring two variants:
  • Kanagawa Wave Blur — dark theme with blur/transparency effects
  • Kanagawa Lotus — light theme with warm, muted tones
• Inspired by the Kanagawa VS Code theme, based on the colors of Katsushika Hokusai's famous painting

Checklist

• Extension ID ends with -theme
• MIT license at repository root
• extensions.toml version matches extension.toml version (0.1.0)
• Submodule uses HTTPS URL
• Ran pnpm sort-extensions
• Theme-only extension (no mixed features)
• ID/name does not contain "zed" or "extension"

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