Display the PM attention count in the sidebar

[kiranfin]

User Story

As a project manager, I want the sidebar to show how many onboarding items require attention, including skip requests and unread feedback.

Context & Motivation

The PM Dashboard entry currently displays an attention marker but no number.

Acceptance Criteria

• The PM Dashboard navigation entry displays the total supplied by the backend.
• Pending skip requests are included.
• Unread onboarding feedback is included.
• A zero count hides the badge.
• The badge updates after a skip decision or feedback acknowledgement.
• The accessible label describes what the number represents.
• Loading and request failures do not display a misleading count.

Technical Notes

Related backend issue: SprintStartProject/sprintstart-backend#243

Confirmed: usePmAttentionFlag (usePmAttentionFlag.ts) is explicitly documented and implemented as a boolean only ("Deliberately a boolean and not a count"), and the sidebar (SideBar.tsx) passes a numeric count only to the Escalation Inbox entry, always 0 for the PM Dashboard entry — so that entry can currently only ever show a dot, never a number (SidebarNavLink.tsx). Consume the dedicated PM-action count from the related backend issue rather than treating the existing blocked/drifting attention endpoint as the same metric.