[FEATURE] Per-run label for Workflow runs in /workflows and task notifications

Problem

When the same workflow script runs several times in parallel (for example one run per GitHub issue), every run shows the same meta.name and meta.description in /workflows and in the background task notification. meta must be a pure literal and the Workflow tool's title/description inputs are ignored, so there is no way to tell which run is which without opening each one.

Opening a run shows phase() titles, agent labels and log() lines, but none of these reach the run list or the notification summary.

Request

A per-invocation label, set by the caller or the script, shown in the /workflows run list and in the task notification summary. Either of:

• a Workflow tool input, e.g. Workflow({ scriptPath, args, runLabel: 'deliver #40' });
• a script API, e.g. setRunLabel('deliver #40'), callable once at the start of the run.

Related (closed as not planned)

• #78632: per-run title missing in the Runs panel
• #82774: naming a run when firing a trigger
• #74419: log() output invisible for background runs

A smaller variant would already help: show the first log() line of a run as its subtitle in the run list.