Fix Plotly £ format warning and add scraper backend selector to Settings

- MarketView: split tickformat '£,.0f' into tickprefix+'£' + tickformat ',.0f' (Plotly d3 format doesn't accept £ prefix inline)
- Settings System tab: add editable dropdown for booking_scraper_backend (hotel page vs search results) with description of the tradeoff; backend was previously read-only in the table

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

frontend/src/pages/MarketView.tsx

@@ -1252,7 +1252,7 @@ const RateHistoryModalComponent: React.FC<{ modal: RateHistoryModal; onClose: ()
                     height: 300,
                     legend: { orientation: 'h', y: -0.25 },
                     xaxis: { title: { text: '' }, tickformat: '%d %b %H:%M', type: 'date' },
-                    yaxis: { title: { text: 'Rate (£)' }, tickformat: '£,.0f' },
+                    yaxis: { title: { text: 'Rate (£)' }, tickprefix: '£', tickformat: ',.0f' },
                     plot_bgcolor: 'var(--body-bg)',
                     paper_bgcolor: 'var(--card-bg)',
                     font: { family: 'inherit', size: 11, color: 'var(--text-dark)' },

frontend/src/pages/Settings.tsx

@@ -798,13 +798,22 @@ function RoomCategoriesCard() {
 // ─── System Tab ───────────────────────────────────────────────────────────────
 
 function SystemTab({ config, isLoading }: { config: SystemConfig | undefined; isLoading: boolean }) {
+  const qc = useQueryClient()
+
+  const saveMutation = useMutation({
+    mutationFn: (payload: { key: string; value: string }) =>
+      api.post('/competitors/config/system', payload),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ['system-config'] }),
+  })
+
   if (isLoading) {
     return <div className="loading-state"><div className="spinner" /> Loading…</div>
   }
 
+  const backend = config?.['booking_scraper_backend'] ?? 'playwright_local'
+
   const displayKeys = [
     'booking_scraper_enabled',
-    'booking_scraper_backend',
     'booking_scraper_daily_time',
     'booking_proxy_enabled',
     'booking_proxy_host',
@@ -815,7 +824,33 @@ function SystemTab({ config, isLoading }: { config: SystemConfig | undefined; is
   ]
 
   return (
-    <div style={{ maxWidth: 700 }}>
+    <div style={{ maxWidth: 700, display: 'flex', flexDirection: 'column', gap: 20 }}>
+      <div className="card">
+        <div className="card-header">Scraper Backend</div>
+        <div className="card-body" style={{ display: 'flex', flexDirection: 'column', gap: 12 }}>
+          <p style={{ fontSize: 13, color: 'var(--text-mid)', margin: 0 }}>
+            Controls how Booking.com rates are fetched. <strong>Hotel page</strong> scrapes each
+            competitor's own property page — captures all room types and rate plan variants (meal
+            plan, cancellation policy, availability). <strong>Search results</strong> scrapes the
+            location search page — faster but only returns the single best-available rate per hotel
+            with no room-type breakdown.
+          </p>
+          <div style={{ display: 'flex', gap: 10, alignItems: 'center' }}>
+            <select
+              style={{ width: 260 }}
+              value={backend}
+              onChange={e => saveMutation.mutate({ key: 'booking_scraper_backend', value: e.target.value })}
+              disabled={saveMutation.isPending}
+            >
+              <option value="playwright_hotel_page">Hotel page (all rooms + rate plans)</option>
+              <option value="playwright_local">Search results (best available only)</option>
+            </select>
+            {saveMutation.isPending && <span style={{ fontSize: 12, color: 'var(--text-mid)' }}>Saving…</span>}
+            {saveMutation.isSuccess && <span style={{ fontSize: 12, color: 'var(--success)' }}>✓ Saved</span>}
+          </div>
+        </div>
+      </div>
+
       <div className="card">
         <div className="card-header">System Configuration</div>
         <div className="table-wrap">
@@ -842,7 +877,7 @@ function SystemTab({ config, isLoading }: { config: SystemConfig | undefined; is
         </div>
       </div>
 
-      <div style={{ marginTop: 16, fontSize: 12, color: 'var(--text-mid)' }}>
+      <div style={{ fontSize: 12, color: 'var(--text-mid)' }}>
         To configure the Booking.com scraper location and hotel tiers, use the Settings tab inside{' '}
         <a href="/rates/market" style={{ color: 'var(--gold)' }}>Market View</a>.
       </div>