⚠️ Improve error reporting and user-friendly messages

[szmyty]

Title: ⚠️ Improve error reporting and user-friendly messages

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Description

Enhance error messages to be clear, actionable, and user-friendly.

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Goals

• Replace raw errors with meaningful messages
• Improve debugging experience

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Requirements

• Wrap errors using "anyhow" context:

.context("Failed to run pandoc")

• Provide:
  • what failed
  • why it failed (if possible)
  • what user can do

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Acceptance Criteria

• Errors are readable and actionable
• No raw panic messages
• Context included in failures