* gui: consistent status page titles and a task icon for the board

Status page titles mixed header and sentence case ("No Workspaces",
"No Tabs" vs "No tasks yet", "No matches"), and the empty Task
Board reused the terminal icon of the "No Workspaces" page. Use header
capitalization for both titles (GNOME HIG writing style) and a list
icon for the board placeholder. Copy and icon only.

Opened by TtyPolish

* spec: match task board empty title (No Tasks Yet)

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Co-authored-by: Lucenx9 <185146821+Lucenx9@users.noreply.github.com>