Add Ayu Dark and Mirage themes

[sor88]

Description of changes:

• Add selectable Ayu Dark and Ayu Mirage application themes.
• Map the official Ayu palettes across UI surfaces, semantic states, logs, and terminal ANSI colors.
• Add matching Monaco editor themes for both variants.
• Register the application and Monaco themes through the explicit DI registries.
• Use Ayu's dark accent.on colors where Freelens components hardcode white foregrounds, preserving readable contrast.

Palette sources:

• https://github.com/ayu-theme/ayu-colors
• https://github.com/ayu-theme/vscode-ayu

Testing:

• pnpm type:check
• pnpm dlx @biomejs/biome@2.5.4 check for all seven changed files
• git diff --check
• Automated validation that every base color comes from the official Ayu Dark or Mirage palettes
• pnpm test:unit:core: 2,506 tests passed; one unrelated terminal API test failed, and one suite could not start after a concurrent Electron binary installation race

[Brainpitcher]

nice one!