Phone Today badge counts agents that Today no longer lists #617

User story

As a phone user, I want the Today button's badge to lead to the agents it counts, so that a number on Today means something I can see there.

Acceptance criteria

• The phone bottom bar shows the Needs-you agent count on a button whose screen lists those agents.
• Tapping that button shows the agents the badge counts.

What I'd notice

The badge moves off Today, or Today's Agents part returns.

Context

#615 removes the Agents part from Today but keeps the badge (AgentBoard.mountBadge), since that issue changes nothing else. When Agents returns to Today this resolves itself.

Found while working #615.

Tasks

• Decide where the badge belongs while Agents is off Today.