feat: add kernel ACPI support for querying battery percentage, add battery indicator to desktop, move log state to 0:/state directory

kernel/src/ACPI/EmbeddedController.hpp

@@ -0,0 +1,50 @@
+/*
+    * EmbeddedController.hpp
+    * ACPI Embedded Controller (PNP0C09) transport
+    * Copyright (c) 2026 Daniel Hammer
+*/
+
+#pragma once
+#include <cstdint>
+
+namespace Hal {
+    namespace EmbeddedController {
+
+        // ============================================================================
+
+        // Bring-up
+
+        // ============================================================================
+        // Locate the EC in the ACPI namespace and latch its command/data ports.
+        // Prefers the ECDT table when present (it is valid before the namespace
+        // is loaded); otherwise walks the namespace for PNP0C09 and reads _CRS.
+        // Safe to call more than once; only the first call does work.
+        void Initialize(void* xsdt);
+
+        // True once a usable command/data port pair has been found.
+        bool IsAvailable();
+
+        // Run the namespace's _REG(EmbeddedControl, 1) methods, telling firmware
+        // that EC region access is live. ACPI requires this once a handler for
+        // an address space is installed, and firmware leans on it hard: EC
+        // methods are typically guarded by a flag that _REG sets, and until it
+        // is set they return safe do-nothing answers (a battery reports itself
+        // absent, a thermal zone reports no temperature). Called by Initialize.
+        void RunRegMethods();
+
+        // Log `bytes` bytes of EC address space starting at `base_`. Purely a
+        // diagnostic: it is the only way to tell a broken handshake from a
+        // register that genuinely reads zero.
+        void DumpSpace(uint8_t base_, int bytes);
+
+        // ============================================================================
+
+        // Transport
+
+        // ============================================================================
+        // Read/write one byte of the EC's 256-byte address space. Both return
+        // false on timeout or when no EC is present, leaving *value untouched.
+        bool Read(uint8_t address, uint8_t& value);
+        bool Write(uint8_t address, uint8_t value);
+    };
+};