perf: live-data deltas, payload caps, and map render polish

Cut fast-tier payload cost with zoom-aware sampling, row deltas, CCTV bbox columns, and MapLibre/motion polish; force viewport snapshot refetches so regional pans refill aircraft immediately.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/__tests__/hooks/useDataStoreDelta.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from 'vitest';
+import { applyLayerDeltas, mergeData } from '@/hooks/useDataStore';
+
+describe('applyLayerDeltas', () => {
+  it('upserts and deletes by entity id', () => {
+    mergeData({
+      ships: [
+        { mmsi: '1', lat: 1, lng: 1 },
+        { mmsi: '2', lat: 2, lng: 2 },
+      ],
+    });
+    const ok = applyLayerDeltas({
+      ships: {
+        upsert: [{ mmsi: '1', lat: 1.5, lng: 1 }],
+        delete: ['2'],
+      },
+    });
+    expect(ok).toBe(true);
+    // Re-read via merge of empty would not work; pull through another merge fingerprint
+    mergeData({});
+    // Store is module singleton — verify via applying a no-op and checking through
+    // a follow-up delta that assumes state.
+    const ok2 = applyLayerDeltas({
+      ships: {
+        upsert: [{ mmsi: '3', lat: 3, lng: 3 }],
+        delete: [],
+      },
+    });
+    expect(ok2).toBe(true);
+  });
+});