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

Assisted-by: GLM 5.3 Flash

docs/man/gasm-dis.1

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+.TH GASM-DIS 1 "2026-09-19" "gasm 0.33.0" "User Commands"
+.SH NAME
+gasm-dis \- disassemble machine code to instruction text
+.SH SYNOPSIS
+.B gasm dis [\-a arch] <file>
+.SH DESCRIPTION
+Disassemble machine code to instruction text, decoded through
+golang.org/x/arch.
+.PP
+With a
+.I .s
+file, the file is assembled first and the listing follows the real
+layout: one block per TEXT function, local labels printed at their
+offsets.  The architecture comes from the file-name suffix, or from
+.BR \-a .
+.PP
+With any other file, or
+.B \-
+for standard input, the bytes are disassembled linearly and
+.B \-a
+selects the architecture (amd64, arm64, riscv64 or loong64).
+.SH OPTIONS
+.TP
+.B \-a \fIarch\fR
+Architecture for raw input: amd64, arm64, riscv64 or loong64.
+.SH EXIT STATUS
+Exits 0 on success, 1 when assembly or decoding fails, and 2 on a usage
+error.
+.SH EXAMPLES
+.nf
+gasm dis k.s                          assemble, then list each function
+gasm dis \-a amd64 \- < dump.bin        disassemble raw bytes from stdin
+.fi
+.SH SEE ALSO
+.BR gasm (1),
+.BR gasm\-asm (1)