Handle non-UTF8 text file encodings for European language support

[lemig]

Description

When processing text files in the document conversion pipeline, we're currently assuming UTF-8 encoding which fails for files using different character encodings common in European languages.

Current Behavior

• The system assumes UTF-8 encoding for all text files
• Files with different encodings (e.g., Windows-1252, ISO-8859-1) fail with UnicodeDecodeError
• Example error:

  UnicodeDecodeError: 'utf-8' codec can't decode byte 0x93 in position 1160: invalid start byte
  

Use Case Context

• Working with digital forensics in a European agency
• Need to handle documents in various European languages
• Files may use different character encodings depending on their origin and creation time

Proposed Solution

Implement a more robust text file reading mechanism that:

1. Attempts to read files with multiple common European encodings:
   • UTF-8
   • Windows-1252 (cp1252)
   • ISO-8859-1
   • Latin-1
2. Provides a fallback mechanism for unrecognized encodings
3. Potentially uses character encoding detection libraries (like chardet)

Technical Details

Current problematic code:

server/app/routes/convert.py (177-178)

# For txt files, just read the content
with open(file_path, 'r', encoding='utf-8') as f:
    content = f.read()