feat(filters): sort number plates A→Z + add assigned-city filter

- Number-plate dropdown now sorted alphabetically (natural/numeric, placeholder
  pinned), re-sorted as live-discovered plates are added.
- New 'Assigned city' filter: populated from the API + live feed, filters the
  live map instantly (with cost centre + plate), auto-fills from a picked
  vehicle, and is passed to the trips query (assigned_city).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

index.html

@@ -299,6 +299,10 @@
         <label for="f-cc">Cost centre</label>
         <select id="f-cc"><option value="">All cost centres</option></select>
       </div>
+      <div class="field">
+        <label for="f-city">Assigned city</label>
+        <select id="f-city"><option value="">All cities</option></select>
+      </div>
       <div class="field">
         <label for="f-period">Time</label>
         <select id="f-period">
@@ -683,6 +687,7 @@ async function loadFilters() {
     const data = await resp.json();
     fillVehicleSelect(data.vehicles || []);
     fillSelect('f-cc', data.cost_centres || []);
+    fillSelect('f-city', data.cities || []);
   } catch (e) { console.error('loadFilters failed:', e); }
 }
 function fillVehicleSelect(vehicles) {
@@ -695,34 +700,53 @@ function fillVehicleSelect(vehicles) {
     opt.value = plate; opt.textContent = v.drivers ? `${plate} — ${v.drivers}` : plate;
     sel.appendChild(opt);
   });
+  sortSelect('f-vehicle');
   sel.addEventListener('change', applyVehicleAutoFilter);
 }
 function fillSelect(id, values) {
   const sel = document.getElementById(id);
   const have = new Set(Array.from(sel.options).map(o => o.value));
-  values.forEach(v => { if (have.has(v)) return; const o = document.createElement('option'); o.value = v; o.textContent = v; sel.appendChild(o); });
+  let added = false;
+  values.forEach(v => { if (have.has(v)) return; const o = document.createElement('option'); o.value = v; o.textContent = v; sel.appendChild(o); added = true; });
+  if (added) sortSelect(id);
 }
-// Add any plate/cc seen in the live feed that the filter-options endpoint missed
+// Reorder a select's options A→Z by value (natural/numeric), keeping any
+// blank-value placeholder ("All …") pinned at the top and preserving selection.
+function sortSelect(id) {
+  const sel = document.getElementById(id);
+  const selected = new Set(Array.from(sel.selectedOptions).map(o => o.value));
+  const opts = Array.from(sel.options);
+  const head = opts.filter(o => o.value === '');
+  const body = opts.filter(o => o.value !== '')
+    .sort((a, b) => a.value.localeCompare(b.value, undefined, { numeric: true, sensitivity: 'base' }));
+  sel.replaceChildren(...head, ...body);
+  Array.from(sel.options).forEach(o => { o.selected = selected.has(o.value); });
+}
+// Add any plate/cc/city seen in the live feed that the filter-options endpoint missed
 function populateFiltersFromLive(features) {
-  const ccs = new Set(), vehSel = document.getElementById('f-vehicle');
+  const ccs = new Set(), cities = new Set(), vehSel = document.getElementById('f-vehicle');
   const havePlates = new Set(Array.from(vehSel.options).map(o => o.value));
+  let addedPlate = false;
   features.forEach(f => {
     const p = f.properties;
     if (p.cost_centre) ccs.add(p.cost_centre);
+    if (p.assigned_city) cities.add(p.assigned_city);
     if (p.vehicle_number && !havePlates.has(p.vehicle_number)) {
       havePlates.add(p.vehicle_number);
       VEHICLE_META.set(p.vehicle_number, { cost_centre: p.cost_centre, assigned_city: p.assigned_city });
-      const o = document.createElement('option'); o.value = p.vehicle_number; o.textContent = p.vehicle_number; vehSel.appendChild(o);
+      const o = document.createElement('option'); o.value = p.vehicle_number; o.textContent = p.vehicle_number; vehSel.appendChild(o); addedPlate = true;
     }
   });
+  if (addedPlate) sortSelect('f-vehicle');
   fillSelect('f-cc', Array.from(ccs).sort());
+  fillSelect('f-city', Array.from(cities).sort());
 }
 function applyVehicleAutoFilter() {
   const sel = document.getElementById('f-vehicle');
   const selected = Array.from(sel.selectedOptions).map(o => o.value);
   const metas = selected.map(p => VEHICLE_META.get(p)).filter(Boolean);
-  const sharedCC = collapse(metas.map(m => m.cost_centre));
-  setSelectValue('f-cc', sharedCC ?? '');
+  setSelectValue('f-cc', collapse(metas.map(m => m.cost_centre)) ?? '');
+  setSelectValue('f-city', collapse(metas.map(m => m.assigned_city)) ?? '');
   applyLiveFilters();   // reflect the plate selection on the live map immediately
 }
 function collapse(values) { if (!values.length) return null; const f = values[0]; return values.every(v => v === f) ? f : null; }
@@ -742,10 +766,11 @@ function applyLiveFilters() {
   if (mode !== 'live') return;
   const plates = new Set(Array.from(document.getElementById('f-vehicle').selectedOptions).map(o => o.value).filter(Boolean));
   const cc = document.getElementById('f-cc').value;
+  const city = document.getElementById('f-city').value;
   let total = 0, moving = 0, parked = 0, offline = 0; const speeds = [];
   (lastLivePayload?.geojson?.features || []).forEach(f => {
     const p = f.properties; const m = liveMarkers.get(p.imei); if (!m) return;
-    const pass = (plates.size === 0 || plates.has(p.vehicle_number)) && (!cc || p.cost_centre === cc);
+    const pass = (plates.size === 0 || plates.has(p.vehicle_number)) && (!cc || p.cost_centre === cc) && (!city || p.assigned_city === city);
     m.getElement().style.display = pass ? '' : 'none';
     if (!pass) return;
     total++;
@@ -761,8 +786,9 @@ function applyLiveFilters() {
 document.getElementById('f-period').addEventListener('change', e => {
   document.getElementById('custom').classList.toggle('show', e.target.value === 'custom');
 });
-// Selecting a cost centre filters the live map immediately.
+// Selecting a cost centre or assigned city filters the live map immediately.
 document.getElementById('f-cc').addEventListener('change', applyLiveFilters);
+document.getElementById('f-city').addEventListener('change', applyLiveFilters);
 function periodToRange(period, cs, ce) {
   const today = new Date(); const fmt = d => d.toISOString().slice(0, 10);
   const minus = n => { const x = new Date(today); x.setDate(x.getDate() - n); return x; };
@@ -780,19 +806,20 @@ function currentFilterSelection() {
   const period = document.getElementById('f-period').value;
   return {
     vehicles, cost_centre: document.getElementById('f-cc').value || '',
+    assigned_city: document.getElementById('f-city').value || '',
     period, start: document.getElementById('f-start').value, end: document.getElementById('f-end').value,
   };
 }
 // "Show trips" button → fleet-wide / multi-vehicle trips from the filter card
 document.getElementById('show-trips').addEventListener('click', () => {
   const sel = currentFilterSelection();
-  enterTrips({ vehicle_numbers: sel.vehicles, cost_centre: sel.cost_centre, period: sel.period, start: sel.start, end: sel.end });
+  enterTrips({ vehicle_numbers: sel.vehicles, cost_centre: sel.cost_centre, assigned_city: sel.assigned_city, period: sel.period, start: sel.start, end: sel.end });
 });
 // Map-dot path → single vehicle, current period in the card
 function enterTripsForVehicle(plate) {
   if (!plate) return;
   const sel = currentFilterSelection();
-  enterTrips({ vehicle_numbers: [plate], cost_centre: '', period: sel.period, start: sel.start, end: sel.end });
+  enterTrips({ vehicle_numbers: [plate], cost_centre: '', assigned_city: '', period: sel.period, start: sel.start, end: sel.end });
 }
 
 // ============================================================================
@@ -812,6 +839,7 @@ async function enterTrips(sel) {
   const params = new URLSearchParams({
     vehicle_numbers: (sel.vehicle_numbers || []).join(','),
     cost_centre: sel.cost_centre || '',
+    assigned_city: sel.assigned_city || '',
     period: sel.period, start_date: range.start_date, end_date: range.end_date,
   });
   try {