feat: Add HTML entity encode/decode and enhance Hex formatting

- Add HTML entity encoding/decoding
- Add Hex formatting options for UTF-8/UTF-16LE encoding
  * Support 7 formats: space/comma/semicolon/0x/\x separators
  * UTF-8 defaults to \x format, UTF-16LE defaults to non-hex
- Improve PreviewDialog
  * Add before/after length display
  * Add Hex output format selector
  * Optimize UI layout
- Bump version to 1.0.5

Init