feat(mnemosyne): add region filter visibility methods to SpatialMemory

- setRegionVisibility(category, visible) — toggle single region
- setAllRegionsVisible(visible) — bulk toggle
- getMemoryCountByRegion() — count memories per category
- isRegionVisible(category) — query visibility state

nexus/components/spatial-memory.js

@@ -1,4 +1,41 @@
-// ═══════════════════════════════════════════
+// ═══
+  // ─── REGION VISIBILITY (Memory Filter) ──────────────
+  let _regionVisibility = {};  // category -> boolean (undefined = visible)
+  
+  setRegionVisibility(category, visible) {
+    _regionVisibility[category] = visible;
+    for (const obj of Object.values(_memoryObjects)) {
+      if (obj.data.category === category && obj.mesh) {
+        obj.mesh.visible = visible !== false;
+      }
+    }
+  },
+
+  setAllRegionsVisible(visible) {
+    const cats = Object.keys(REGIONS);
+    for (const cat of cats) {
+      _regionVisibility[cat] = visible;
+      for (const obj of Object.values(_memoryObjects)) {
+        if (obj.data.category === cat && obj.mesh) {
+          obj.mesh.visible = visible;
+        }
+      }
+    }
+  },
+
+  getMemoryCountByRegion() {
+    const counts = {};
+    for (const obj of Object.values(_memoryObjects)) {
+      const cat = obj.data.category || 'working';
+      counts[cat] = (counts[cat] || 0) + 1;
+    }
+    return counts;
+  },
+
+  isRegionVisible(category) {
+    return _regionVisibility[category] !== false;
+  },
+════════════════════════════════════════
 //  PROJECT MNEMOSYNE — SPATIAL MEMORY SCHEMA
 // ═══════════════════════════════════════════
 //