feat: implement kernel capability model

kernel/src/Memory/UserRange.hpp

@@ -0,0 +1,23 @@
+/*
+    * UserRange.hpp
+    * Cross-CPU invalidation and teardown of user address-space mappings
+    * Copyright (c) 2026 Daniel Hammer
+*/
+
+#pragma once
+#include <cstdint>
+
+namespace Memory {
+
+    // Register the TLB-shootdown IPI handler. Must run before any AP is
+    // booted, since a shootdown targets every CPU running the address space.
+    void InitUserRange();
+
+    // Invalidate a user range on every CPU currently running the address
+    // space. Call this after removing PTEs and before releasing their frames.
+    void ShootdownUserRange(uint64_t pml4Phys, uint64_t startVa, uint32_t pages);
+
+    // Safely remove ordinary PFA-backed user mappings and release their frames.
+    void UnmapAndFreeUserRange(uint64_t pml4Phys, uint64_t startVa, uint64_t pages);
+
+}