vt: keep OSC 8 links when the URL contains semicolons

## Problem

An OSC 8 hyperlink is discarded when its URL contains a semicolon.

Only the first two semicolons in an OSC 8 command separate fields. Any later semicolons are part of the URL.

## Minimal reproduction

Using `github.com/charmbracelet/x/vt` at `3755ebad01b1`, write this sequence:

```text
ESC ] 8 ; ; https://example.com/f?a=1;b=2 ESC \ L3 ESC ] 8 ; ; ESC \
```

In Go:

```go
_, _ = emu.Write([]byte("\x1b]8;;https://example.com/f?a=1;b=2\x1b\\L3\x1b]8;;\x1b\\"))
```

## Expected

The cells for `L3` should have this link URL:

```text
https://example.com/f?a=1;b=2
```

## Actual

The link is not attached to the cells. The parser splits at every semicolon and rejects the command when it gets more than three pieces.

## Suggested direction

Split only at the first two semicolons. The remainder belongs to the URL.

## Why this matters

URLs can legally use semicolons, including in query strings and path parameters. The visible text still renders, but the link is no longer clickable.

PR #868 fixes a separate OSC 8 problem where the URL and parameter fields are exchanged. That fix makes ordinary links correct, but URLs containing semicolons still fail.

Start in the github.com/charmbracelet/x/vt OSC 8 parsing path reached by emu.Write, using the minimal reproduction in this issue to observe how semicolons are handled. The work is done when the L3 cells retain the full URL https://example.com/f?a=1;b=2 while the visible text still renders.

Written by the indexing model from the issue text.