Harden unicode/exif handling and sanitize generated paths

[TerryFrench]

Summary

This PR improves import robustness for files with unicode metadata and for generated output names that contain path-unsafe characters.

Changes

• Harden ExifTool/media metadata handling to avoid crashes on unicode decode edge cases.
• Sanitize generated file/folder path components to prevent invalid separators and invalid filename characters (especially important on Windows).
• Add regression tests for:
  • non-ASCII filename/exif handling
  • generated-name/path sanitization

Why

Some real-world media contains unicode values and title/location text that can produce invalid paths or trigger metadata parsing failures. This caused imports to fail on certain files.

Scope

• Focused on resilience and cross-platform path safety.
• No intentional behavior change for normal/valid metadata values.

Validation

• Local test run: 338 passed, 4 skipped, 1 xfailed (warnings only).