Add Bluetooth HID remote control support

Integrate BLE keyboard host functionality for page-turner remotes. Adds device pairing, button mapping, preset configurations for Free2/Free3 remotes, and persistent storage of mappings. Migrates from open-x4-sdk to freeink-sdk submodule which includes the BleKeyboardHost library. Implements CPU frequency locking during BLE operations to prevent watchdog timeouts.

src/BleInput.h

@@ -0,0 +1,41 @@
+#pragma once
+
+// CrossPoint <-> FreeInk BLE HID host glue.
+//
+// Thin, capability-safe helpers around freeink::BleKeyboardHost (the `BleHid`
+// singleton). When FREEINK_CAP_BLE_HID_HOST is compiled out the SDK links stubs,
+// so every call here is still valid and simply no-ops / returns false — callers
+// need no #ifdefs.
+//
+// The (kind, value) pair produced by encodeKey() is the stable identity stored in
+// CrossPointSettings::bleKeyMap. Page-turner remotes emit "special" keys
+// (PageUp/PageDown/arrows); plain keyboards emit usage codes. We deliberately
+// ignore modifiers and the printable char for matching (page turners don't use
+// modifiers), keeping the persisted entry a trivial two-byte comparison.
+
+#include <BleKeyboardHost.h>
+
+#include <cstdint>
+
+namespace bleinput {
+
+// Advertised central name shown to peripherals during pairing.
+inline constexpr const char* kHostName = "CrossPoint";
+
+// Start the BLE HID host (idempotent). Returns false if BLE is compiled out or
+// NimBLE init failed. Safe to call repeatedly.
+bool ensureStarted();
+
+// Drop the active link (e.g. before deep sleep or when the user disables BT).
+void stop();
+
+// Encode a decoded key event into the stable (kind, value) identity used by the
+// settings map. kind: 0 = SpecialKey, 1 = HID usage. Returns false when the event
+// carries no usable identity (no special key and no usage code).
+bool encodeKey(const freeink::KeyEvent& ev, uint8_t& kind, uint8_t& value);
+
+// Human-readable name for a stored (kind, value) identity, for the mapping UI.
+// Writes a null-terminated string into out (e.g. "Page Down", "Key 0x4B").
+void describeKey(uint8_t kind, uint8_t value, char* out, size_t outLen);
+
+}  // namespace bleinput