feat: live pipeline activity log + on-shift roster

[Goodnight77]

Live activity log (SSE) showing the fault->fix pipeline in real time, plus roster wired to real on-shift technicians for live WhatsApp dispatch.

• Backend: live.push_activity ring buffer; stages emitted (fault_received, diagnosing, work_order_created, approved, dispatched, rejected, dispatch_failed); SSE at /events/activity/stream + REST /events/activity/recent
• Frontend: ActivityLog panel on the dashboard via EventSource (no polling), newest-first, color-coded stages
• Roster: 3 real numbers on-shift covering all skills (electromechanical/packaging/general); 2 placeholder-number techs parked off-shift until real numbers provided
• Verified: approve -> routing -> real Twilio WhatsApp send (SID returned)