refactor(scripts): Use `#!/usr/bin/env` as part of shebang

This resolves build errors in systems like NixOS, where `/bin/bash`
doesn't exist.

backup.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 BKPPATH="firmware-backups"
 

build.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 if make -j "$(nproc)" T=open_source DEBUG=1 >log.txt 2>&1; then
 	echo "build success"

clear.sh

@@ -1,3 +1,3 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 make -j "$(nproc)" T=open_source DEBUG=1 clean

convert.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 txt_to_wav() {
   hash="$(md5sum "$1" | cut -d ' ' -f 1)"

download.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 
 num=$(find /dev -name 'ttyACM*' | sort | rev | cut -c 1)
 echo com is: "$num"

start_dev.sh

@@ -1,2 +1,2 @@
-#!/bin/sh
+#!/usr/bin/env sh
 docker-compose run --rm builder

uart_log.sh

@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/usr/bin/env sh
 
 num=$(find /dev -name 'ttyUSB*' | rev | cut -c 1)
 echo "$num"