feat(docs): man pages for gasm and every command, guarded against CLI drift

Assisted-by: GLM 5.3 Flash

docs/man/gasm-scaffold.1

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+.TH GASM-SCAFFOLD 1 "2026-09-19" "gasm 0.33.0" "User Commands"
+.SH NAME
+gasm-scaffold \- generate a differential test skeleton for a kernel file
+.SH SYNOPSIS
+.B gasm scaffold differential <file.s>
+.SH DESCRIPTION
+Print a differential test skeleton for every
+.B //\ func
+signature in FILE.  The test seeds random states, drives the kernel and
+a portable reference (\fI<name>Portable\fR), and compares outputs
+byte-for-byte.  Write the reference bodies, place the file in the
+kernel's package, and run it in CI.
+.SH EXIT STATUS
+Exits 0 when the skeleton is written to stdout and 1 when the file
+cannot be parsed; a usage error exits 2.
+.SH EXAMPLES
+.nf
+gasm scaffold differential kernel_amd64.s > kernel_differential_test.go
+.fi
+.SH SEE ALSO
+.BR gasm (1),
+.BR gasm\-verify (1)