refactor: Add more checks to pre-commit

Updated existing pre-commit hooks and added some new hooks:

- Remove trailing whitespace
- Ensure every non-empty file ends with a new line
- Check YAML file validity
- Prevent adding large files
- Ensure any scripts with shebangs are executable

Added a GitHub action to run pre-commit on every commit. Removed any
existing actions which duplicate pre-commit.

Ran pre-commit on the codebase.

app/boards/shields/tg4x/README.md

@@ -6,6 +6,6 @@ Standard setup for the [TG4x](https://github.com/MythosMann/tg4x/) 40% keyboard.
 
 This TG4x implementation is for...
 
-* rev 2.1 of the board
-* Split spacebar with 2.25U on the left and 2.75U on the right
-* 2U right shift
+- rev 2.1 of the board
+- Split spacebar with 2.25U on the left and 2.75U on the right
+- 2U right shift

app/boards/shields/tg4x/tg4x.overlay

@@ -10,7 +10,7 @@
 	kscan0: kscan {
 		compatible = "zmk,kscan-gpio-matrix";
 		label = "KSCAN";
-		
+
 		diode-direction = "col2row";
 
 		row-gpios