fix(frontend): handle NaN in parseUploadedFiles size parsing

[hobostay]

Fixes #1794

Problem

The parseUploadedFiles function in frontend/src/core/messages/utils.ts
uses parseInt(fileMatch[2].trim(), 10) ?? 0 to parse file sizes. However,
the nullish coalescing operator (??) only handles null and undefined,
not NaN. When the size string cannot be parsed as a valid integer,
parseInt returns NaN, which is not caught by ??, causing the file
size to be NaN instead of 0.

Root Cause

• parseInt('invalid', 10) returns NaN (not null or undefined)
• The ?? operator only checks for null/undefined, not NaN
• Invalid size strings result in NaN being stored as the file size

Fix

Split the parsing into a separate step and use isNaN() to explicitly
check for NaN values:

const size = parseInt(fileMatch[2].trim(), 10);
files.push({
  filename: fileMatch[1].trim(),
  size: isNaN(size) ? 0 : size,
  path: fileMatch[3].trim(),
});

This ensures that any non-numeric size values default to 0 instead of
NaN.

Test Case

Before this fix, calling parseUploadedFiles with content like:

<uploaded_files>- file.txt (invalid_size)
  Path: /path/to/file</uploaded_files>

Would result in { filename: "file.txt", size: NaN, path: "/path/to/file" }.

After this fix, the result is:
{ filename: "file.txt", size: 0, path: "/path/to/file" }.

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