[Keyboard] Add Quefrency LM Rev. 1 (#25692)

* Initial WIP commit

* Update right half pins

* Update RGB matrix and layout

* Enable more RGB animations

* Update license headers

* Cleanup keymap and RGB

* Move handedness pin definition, cleanup RGB defines

* Adjust keymap

keyboards/keebio/quefrency_lm/info.json

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+{
+    "manufacturer": "Keebio",
+    "url": "https://keeb.io",
+    "maintainer": "nooges",
+    "usb": {
+        "vid": "0xCB10"
+    },
+    "features": {
+        "bootmagic": true,
+        "console": true,
+        "extrakey": true,
+        "mousekey": true,
+        "nkro": false
+    },
+    "split": {
+        "enabled": true
+    },
+    "build": {
+        "lto": true
+    }
+}

keyboards/keebio/quefrency_lm/keymaps/default/keymap.c

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+// Copyright 2025 Keebio (@keebio)
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include QMK_KEYBOARD_H
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+  [0] = LAYOUT_65xt(
+    KC_F1,   KC_F2,   QK_GESC, KC_1,    KC_2,    KC_3,    KC_4,    KC_5,    KC_6,    KC_7,    KC_8,    KC_9,    KC_0,    KC_MINS, KC_EQL,  KC_BSPC, KC_DEL,
+    KC_F3,   KC_F4,   KC_TAB,  KC_Q,    KC_W,    KC_E,    KC_R,    KC_T,    KC_Y,    KC_U,    KC_I,    KC_O,    KC_P,    KC_LBRC, KC_RBRC, KC_BSLS, KC_HOME,
+    KC_F5,   KC_F6,   KC_CAPS, KC_A,    KC_S,    KC_D,    KC_F,    KC_G,    KC_H,    KC_J,    KC_K,    KC_L,    KC_SCLN, KC_QUOT,          KC_ENT,  KC_PGUP,
+    KC_F7,   KC_F8,   KC_LSFT,          KC_Z,    KC_X,    KC_C,    KC_V,    KC_B,    KC_N,    KC_M,    KC_COMM, KC_DOT,  KC_SLSH, KC_RSFT, KC_UP,   KC_PGDN,
+    KC_F9,   KC_F10,  KC_LCTL, KC_LALT, KC_LGUI, MO(1),   KC_SPC,                             KC_SPC,  KC_RALT, MO(1),   KC_RCTL, KC_LEFT, KC_DOWN, KC_RGHT
+  ),
+  [1] = LAYOUT_65xt(
+    RM_HUEU, RM_HUED, KC_GRV,  KC_F1,   KC_F2,   KC_F3,   KC_F4,   KC_F5,   KC_F6,   KC_F7,   KC_F8,   KC_F9,   KC_F10,  KC_F11,  KC_F12,  _______, _______,
+    RM_SATU, RM_SATD, RM_TOGG, RM_NEXT, KC_UP,   _______, QK_BOOT, _______, _______, _______, _______, _______, _______, _______, _______, _______, KC_END,
+    RM_VALU, RM_VALD, _______, KC_LEFT, KC_DOWN, KC_RGHT, _______, _______, _______, _______, _______, _______, _______,          _______, _______, _______,
+    RM_SPDU, RM_SPDD, _______,          _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______, _______,
+    _______, _______, _______, _______, _______, _______, _______,                            _______, _______, _______, _______, _______, _______, _______
+  )
+};

keyboards/keebio/quefrency_lm/readme.md

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+# Quefrency LM
+
+A split 65XT staggered low-profile keyboard made and sold by Keebio. [More info at Keebio](https://keeb.io).
+
+* Keyboard Maintainer: [Bakingpy/nooges](https://github.com/nooges)
+* Hardware Availability: [Keebio](https://keeb.io/)
+
+Make example for this keyboard (after setting up your build environment):
+
+    make keebio/quefrency_lm/rev1:default
+
+Example of flashing this keyboard:
+
+    make keebio/quefrency_lm/rev1:default:flash
+
+Handedness detection is already hardwired onto the PCB, so no need to deal with `EE_HANDS` or flashing .eep files.
+
+See the [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) and the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information. Brand new to QMK? Start with our [Complete Newbs Guide](https://docs.qmk.fm/#/newbs).
+
+## Bootloader
+
+Enter the bootloader in one of these ways:
+
+* **Physical reset button**: Press and hold the button on the back of the PCB for at least 2 seconds and let go, or double-press the button
+* **Keycode in layout**: Press the key mapped to `QK_BOOT` if it is available
+
+A build guide for this keyboard can be found here: [Keebio Build Guides](https://docs.keeb.io)

keyboards/keebio/quefrency_lm/rev1/config.h

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+// Copyright 2025 Keebio (@keebio)
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+/* Defines for the split keyboard setup */
+#define SERIAL_USART_DRIVER SD3         // USART 3
+#define SERIAL_USART_TX_PIN B10
+#define SERIAL_USART_RX_PIN B11
+#define SERIAL_USART_TX_PAL_MODE 7
+#define SERIAL_USART_RX_PAL_MODE 7
+#define SERIAL_USART_FULL_DUPLEX
+#define SERIAL_USART_PIN_SWAP
+
+#define USB_VBUS_PIN C6
+
+/* Defines for the RGB matrix */
+#define WS2812_PWM_DRIVER PWMD3
+#define WS2812_PWM_CHANNEL 4
+#define WS2812_PWM_PAL_MODE 10
+#define WS2812_DMA_STREAM STM32_DMA1_STREAM2
+#define WS2812_DMA_CHANNEL 2
+#define WS2812_DMAMUX_ID STM32_DMAMUX1_TIM3_UP

keyboards/keebio/quefrency_lm/rev1/halconf.h

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+// Copyright 2025 Keebio (@keebio)
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#define HAL_USE_SERIAL TRUE
+
+#define HAL_USE_PWM TRUE
+
+#include_next <halconf.h>

keyboards/keebio/quefrency_lm/rev1/mcuconf.h

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+// Copyright 2025 Keebio (@keebio)
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include_next <mcuconf.h>
+
+/* enable USART3, used for split comms */
+#undef STM32_SERIAL_USE_USART3
+#define STM32_SERIAL_USE_USART3 TRUE
+
+/* enable TIM3, used for RGB LED PWM driver */
+#undef STM32_PWM_USE_TIM3
+#define STM32_PWM_USE_TIM3 TRUE

keyboards/keebio/quefrency_lm/rev1/rev1.c

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+// Copyright 2025 Keebio (@keebio)
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "quantum.h"
+
+void keyboard_pre_init_kb(void) {
+    // Disable the PD peripheral in pre-init because its pins are being used in the matrix:
+    PWR->CR3 |= PWR_CR3_UCPD_DBDIS;
+    // Call the corresponding _user() function (see https://docs.qmk.fm/#/custom_quantum_functions)
+    keyboard_pre_init_user();
+}