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_checksum.md

@@ -1 +1,38 @@
-# Placeholder
+# compile_checksum.sh
+
+Generates MD5 checksums for all Pascal source files.
+
+## Overview
+
+`compile_checksum.sh` iterates over every `.pas` file under `src/` and appends its MD5 hash to `checksums.md5`. This file serves as a source-level fingerprint used by `compile_vergen.sh` to produce a build integrity checksum.
+
+## Prerequisites
+
+- `md5sum` and `find` must be available.
+- The `src/` directory must exist and contain `.pas` files.
+
+## Inputs
+
+All `*.pas` files found recursively under `src/`, up to 10 levels deep.
+
+## Outputs
+
+| File | Description |
+|------|-------------|
+| `checksums.md5` | A file containing one `md5sum`-format line per Pascal source file. |
+
+## Behavior
+
+1. Truncates (or creates) `checksums.md5` with an empty write (`echo >`).
+2. Finds all directories under `src/` (up to 10 levels deep).
+3. For each directory, iterates over `*.pas` files and computes their MD5 checksum.
+4. Skips files matching any of the following conditions:
+   - Path contains `.svn` (Subversion metadata).
+   - The glob matched no files (literal `*.pas` string).
+   - Path contains `include/asuro.pas`.
+5. Appends each valid checksum line to `checksums.md5`.
+
+## Notes
+
+- The resulting `checksums.md5` is consumed by `compile_vergen.sh`, which hashes the checksum file itself to produce a single build fingerprint constant embedded in the kernel.
+- The `.svn` exclusion is a legacy filter from when the project used Subversion for version control.