Add 5-tier warning thresholds to staff rota footer

Replaces the 2-row (vs Booked / vs with Pickup) footer with a progressive 5-row breakdown:
- Total Available (unchanged)
- vs Booked — plain diff, room cleaning only
- with Recurring Tasks — plain diff, adds recurring tasks
- with Pickup — plain diff, adds pickup hours
- with Adjustments — bold coloured final row with configurable thresholds

New 5-tier icon system: red ⚠ / amber ⚠ / green ✓ / amber ✗ / red ✗, with defaults of
4h / 1h / 1h / 2h spare or short. Thresholds are editable in Settings.

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

frontend/src/api.ts

@@ -8,10 +8,13 @@ export interface ConfigData {
   pickup_data: PickupData
   general_tasks: GeneralTask[]
   last_reviewed: string
-  tolerance_minutes: number
   workforce_rota: WorkforceRota | null
   workforce_departments: string[]
   adjustments: Adjustment[]
+  warn_over_red_hrs: number
+  warn_over_amber_hrs: number
+  warn_under_amber_hrs: number
+  warn_under_red_hrs: number
 }
 
 export interface CategoryConfig {
@@ -129,3 +132,16 @@ export function putAdjustments(adjustments: Adjustment[]): Promise<{ ok: boolean
     body: JSON.stringify({ adjustments }),
   })
 }
+
+export function putWarningThresholds(thresholds: {
+  warn_over_red_hrs: number
+  warn_over_amber_hrs: number
+  warn_under_amber_hrs: number
+  warn_under_red_hrs: number
+}): Promise<{ ok: boolean }> {
+  return request('/config/warning-thresholds', {
+    method: 'PUT',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(thresholds),
+  })
+}