Add file attachments to chat input box

[fkn1987]

Summary

Adds the ability to attach non-image files (e.g. PDFs, text, archives) to the chat input box.

Changes

• New \FileMessagePart\ type in core (\core/index.d.ts\ + \core/config/types.ts) carrying
  ame\ and \dataUrl.
• Choke point: \constructMessages\ converts file parts to a text placeholder ([Attachment: name]) before messages reach any LLM provider, so providers never receive an unsupported part type.
• Defense in depth for file parts in: \countTokens, \openaiTypeConverters\ (Chat Completions + Responses paths), \Anthropic, \Gemini, \stripImages, and console \Message\ rendering.
• Editor: new TipTap \FileAttachment\ inline node with a NodeView chip (name + download via dataUrl), paste/drop handling for non-image files, and a paperclip toolbar button.

Tests

• \constructMessages.test.ts: file parts are converted to [Attachment: name]\ without leaking the dataUrl; messages without file parts are unchanged.
• \countTokens.test.ts: counting tokens for file parts does not throw.

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[fkn1987]

Fechando — projeto errado. Desculpe o incômodo.