Initial port of stecman/hw-boot-selection to ESP32-S3

ESPHome external_component that presents a synthetic 64 KB FAT12 disk
over the ESP32-S3's native USB-OTG, containing a one-byte switch_position
file and a switch_position_grub.cfg snippet.  The disk's volume serial
is fixed at 0x55AA6922 to stay drop-in compatible with the upstream
/etc/grub.d hook.

Components:
- fat12 / msc_disk: portable FAT12 sector synthesiser ported from
  reference/src/fat.c and the boot-sector / FAT / dir-entry generation
  in reference/src/usb.c.
- usb_descriptors / tusb_glue: TinyUSB MSC class with our own callbacks
  delegating to MscDisk::read_lba (linker --allow-multiple-definition
  picks ours over esp_tinyusb's storage-backed defaults).
- grub_boot_switch: top-level Component, NVS persistence on target
  changes, exposes targets table to sub-platforms.
- select: HA-facing select platform reading parent's targets map.

Validated end-to-end on an ESP32-S3-DevKitC-1: USB enumerates as
26ba:8003, /dev/sdb mounts FAT12, mtype reads back the live target,
and POST /select/boot_target/set?option=Windows updates both files
on the next host read.

components/grub_boot_switch/select/boot_target_select.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/select/select.h"
+
+#include "../grub_boot_switch.h"
+
+namespace esphome {
+namespace grub_boot_switch {
+
+class BootTargetSelect : public select::Select, public Component {
+ public:
+  void set_parent(GrubBootSwitch *parent) { parent_ = parent; }
+
+  void setup() override;
+
+ protected:
+  void control(const std::string &value) override;
+
+  GrubBootSwitch *parent_{nullptr};
+};
+
+}  // namespace grub_boot_switch
+}  // namespace esphome