Fix shift hours overcounting automatic breaks + add version-check banner

Workforce's automatic_break_length is a payroll deduction setting, not a
scheduling field — applying it when no explicit breaks are present was silently
shortening all shifts (e.g. a 2h shift showing as 1.5h). Now only deducts
explicit break records from s.breaks. Also adds BUILD_VERSION to /health and
an UpdateBanner that prompts staff to reload when a new deploy lands.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/lib/workforce.js

@@ -95,8 +95,6 @@ export async function fetchShifts(from, to, deptIds) {
     let breakHrs = 0
     if (Array.isArray(s.breaks) && s.breaks.length) {
       breakHrs = s.breaks.reduce((sum, b) => sum + (b.finish - b.start) / 3600, 0)
-    } else {
-      breakHrs = (s.automatic_break_length ?? 0) / 60
     }
     const shiftHrs = Math.max(0, (s.finish - s.start) / 3600 - breakHrs)