[FEATURE] Emit OSC 8 hyperlinks for URLs in task-list widget subjects

Feature request

Emit OSC 8 hyperlinks for URLs appearing in task subjects when rendering the
persistent task-list widget (the TaskCreate/TaskUpdate panel).

Current behavior

A task subject containing a URL, e.g.

#4. Review dep-bump PR — https://github.com/org/repo/pull/123

renders in the task widget as plain styled text. The URL is not clickable.

Why terminal-side URL detection can't compensate

1. Claude Code enables mouse reporting, so the terminal emulator's own

URL-regex click detection (e.g. iTerm2 Cmd+click) doesn't reliably reach
the widget text (related: #73766).

1. The widget truncates long subjects at the right edge. A truncated URL is

incomplete text, so no terminal-side regex can ever match it — only an
application-emitted OSC 8 sequence can carry the full URI for a partially
visible label.

Point 2 is also why OSC 8 here is strictly better than relying on the
terminal: with OSC 8, the visible (possibly truncated) subject text can still
link to the complete URL.

Evidence the machinery already exists

• Bare URLs in response markdown are already emitted as OSC 8 hyperlinks

(noted as the working case in #69570).

• File paths in tool-call headers are wrapped in OSC 8 file:// links

(#69008 asks to extend that to plain-text output).

• The hyperlink capability check already special-cases tmux ≥ 3.4

(TERM_PROGRAM=tmux + version parse), so emission is correctly enabled in
tmux environments.

The task widget appears to be the only list surface where user-authored text
containing URLs is rendered without going through any linkification path.

Use case

Tracking open PRs as tasks, with each task subject ending in its PR URL. The
task widget is the always-visible surface; jumping to a PR currently requires
finding the same URL elsewhere in the transcript.

Environment

• Claude Code 2.1.208
• iTerm2 3.6.11 + tmux 3.6a (both OSC 8-capable; tmux ≥ 3.4 forwards

hyperlinks natively — other Claude Code surfaces confirm emission works in
this stack)

• macOS (darwin 25.5.0)