fix(vt): store OSC 8 hyperlink params and uri in correct fields

[paultyng]

Summary

handleHyperlink stores the OSC 8 params slot into Link.URL and the URI slot into Link.Params. The two fields are swapped.

Problem

OSC 8 wire format:

ESC ] 8 ; <params> ; <uri> ST

After bytes.Split(data, ';') on valid 8;<params>;<uri> input, parts[1] is <params> and parts[2] is <uri>. The handler does the opposite.

Impact

Any consumer that round-trips cells back to ANSI via ansi.SetHyperlink(cell.Link.URL, cell.Link.Params) re-emits with the slots swapped. The common case ESC]8;;<uri>ST becomes ESC]8;<uri>;ST — URI in the params slot, URI slot empty. xterm.js's parser rejects it via the empty-URI branch; the styled text renders but is not clickable.

In-repo: cellbuf follows this exact pattern at
screen.go:734,
wrap.go:90,
pen.go:66,
writer.go:126,
so any cellbuf consumer whose cells were populated by vt inherits the swap.

Common emitters of OSC 8 whose output would round-trip incorrectly:
GNU coreutils ls --hyperlink,
ripgrep,
fd.

Changes

vt/osc.go: swap the two assignments.
vt/osc_test.go (new): two subtests via Emulator.CellAt(0,0).Link,
covering empty-params and populated-params forms. Both fail on main
with field-value assertions surfacing the swap; pass with the fix.

Testing

go test -race ./vt/... passes locally; CI covers Linux/macOS/Windows.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 36.90%. Comparing base (798e623) to head (a33b01e).
⚠️ Report is 29 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #868      +/-   ##
==========================================
- Coverage   38.14%   36.90%   -1.25%     
==========================================
  Files         196       21     -175     
  Lines       16750     1837   -14913     
==========================================
- Hits         6390      678    -5712     
+ Misses       9959     1070    -8889     
+ Partials      401       89     -312     

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