docs: fill out compat, lvglh, and toolchain documentation

Replace placeholder content in doc/compat/, doc/lvglh/, and
doc/toolchain/ with comprehensive documentation derived from the
source files.

- compat: document Wasuro WASM VM compatibility shims
- lvglh: document LVGL v9.2.2 configuration, fonts, and patches
- toolchain: document all 13 build pipeline scripts

doc/toolchain/compile_stub.md

@@ -1 +1,37 @@
-# Placeholder
+# compile_stub.sh
+
+Assembles the low-level boot stub and splash screen objects.
+
+## Overview
+
+`compile_stub.sh` uses NASM to assemble two assembly source files into ELF object files. These objects contain the initial boot entry point and an embedded splash-screen TGA image, both of which are linked into the final kernel binary.
+
+## Prerequisites
+
+- `nasm` must be available on the PATH.
+- The source files `src/arch/x86/boot/stub.asm` and `src/boot/splash_tga.asm` must exist.
+- The `lib/` output directory must exist (created by `compile.sh` which clears it beforehand).
+
+## Inputs
+
+| File | Description |
+|------|-------------|
+| `src/arch/x86/boot/stub.asm` | x86 boot stub -- the kernel entry point before Pascal code takes over. |
+| `src/boot/splash_tga.asm` | Embeds a TGA splash screen image as a binary blob. |
+
+## Outputs
+
+| File | Description |
+|------|-------------|
+| `lib/stub.o` | ELF object for the boot stub. |
+| `lib/splash_tga.o` | ELF object for the splash screen data. |
+
+## Behavior
+
+1. Assembles `stub.asm` into `lib/stub.o` using NASM with the ELF output format (`-f elf`).
+2. Assembles `splash_tga.asm` into `lib/splash_tga.o` using the same format.
+
+## Notes
+
+- Both files are assembled as 32-bit ELF objects, consistent with the i386 target architecture.
+- `stub.o` is treated specially during linking: `compile_link.sh` places it first in the link order so that the boot entry point appears at the expected address.