feat: pré-visualização completa, tema, nova identidade e correções (0.2.0)

- Preview de imagem, vídeo/MP4, áudio, PDF (pdf.js), texto, Office/ODF, ZIP e hex,
  lido sob demanda com Range; tela cheia com navegação por teclado.
- Seletor de tema Auto/Claro/Escuro persistido (vale também como administrador).
- Identidade verde-azulada com logo de pixels que formam um lobo.
- Corrige reinício como administrador no AppImage (usa $APPIMAGE) e mostra o motivo.
- Corrige barra inferior piscando (render idempotente, barra criada uma vez).
- Corrige FAT32 em mídias pequenas não reconhecido.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

apps/gui/ui/guara.svg

@@ -1,17 +1 @@
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-  </defs>
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-  <!-- orelhas grandes e focinho longo do lobo-guará -->
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-  <path d="M98 22 L76 50 L90 62 Z" fill="#fff"/>
-  <path d="M38 62 L52 50 Q64 44 76 50 L90 62 L74 96 Q64 108 54 96 Z" fill="#fff"/>
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-</svg>
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