Found this while looking into a markdown preview issue. Clicking a
`path:row:column` target in the terminal treated the column as a byte
offset, so on lines with non-ASCII characters the cursor landed at mid
codepoint.

The real fix is just 3 lines and the rest is a refactor that extracts
the open and navigate logic so it can be reused later for cases like
markdown preview.

Release Notes:

- Fixed the cursor landing at the wrong column when clicking a
`path:row:column` link in the terminal for lines containing non-ASCII
characters.