feat(man): generate rendered man page reference file

Add a step to generate-completions.sh that produces exports/pdu.1.man,
the plain-text rendering of the man page (via MANWIDTH=80 man), for
reference and AI review alongside the existing help text files.

https://claude.ai/code/session_01CrXuWDMVQsiUBoy6ceACsF

Author: claude

generate-completions.sh

@@ -18,3 +18,4 @@ gen elvish completion.elv
 ./run.sh pdu -h | sed 's/[[:space:]]*$//' > exports/short.help
 ./run.sh pdu-usage-md > USAGE.md
 ./run.sh pdu-man-page > exports/pdu.1
+MANWIDTH=80 man ./exports/pdu.1 | sed 's/[[:space:]]*$//' > exports/pdu.1.man