Fix timesheet sync overwriting future rota dates with empty data

Pull timesheets was writing source='timesheet' rows for future dates
(no clock-in data yet), giving ? / 0.00h and preventing rota sync
from ever healing those dates.

Three-part fix:
- Backend runTimesheetSync: cap end date to today before looping
- Frontend syncTimesheetData: cap end date to today before calling API
- Backend runRotaSync: only skip timesheet-sourced dates that are <= today,
  so any future dates accidentally marked as timesheet are self-healed
  next time rota sync runs

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

backend/src/lib/syncJobs.js

@@ -56,10 +56,13 @@ export async function runRotaSync(from, to) {
     }
   }
 
-  // Skip dates already replaced with timesheet actuals
+  // Skip past dates already replaced with timesheet actuals (future timesheet rows are allowed through)
+  const today = fmtDate(new Date())
   const existing = await getWorkforceShifts(from, to)
   const timesheetDates = new Set(
-    Object.entries(existing).filter(([, d]) => d.source === 'timesheet').map(([date]) => date)
+    Object.entries(existing)
+      .filter(([date, d]) => d.source === 'timesheet' && date <= today)
+      .map(([date]) => date)
   )
 
   const dailyRows = []
@@ -81,6 +84,10 @@ export async function runTimesheetSync(from, to) {
 
   if (!from || !to) ({ from, to } = defaultTimesheetWindow())
 
+  // Never write timesheet rows for future dates — actual hours don't exist yet
+  const today = fmtDate(new Date())
+  if (to > today) to = today
+
   const fromDate = new Date(from + 'T00:00:00')
   const toDate   = new Date(to   + 'T00:00:00')