build: extract halcompile manpages via adoc, drop troff sed hacks

[grandixximo]

Summary

Per @BsAtHome's review on #4086. The old COMP_MANPAGES /
COMP_DRIVER_MANPAGES rules ran halcompile --document (troff straight
out) and sed-escaped .als / .URL groff directives the old dblatex
PDF pipeline could not parse. Asciidoctor now reads the component
adoc directly, so the sed hacks are obsolete.

New chain:

• halcompile --adoc -o objects/man/man9/<comp>.9.adoc <comp>.comp
• asciidoctor --doctype=manpage --backend=manpage -> ../docs/man/man9/<comp>.9

The adoc extraction only needs Python + halcompile.py (yapps-generated,
not the C build), so a fresh-tree docs-only build (make htmldocs /
pdfdocs / docs) extracts and renders component manpages without
first compiling the rest of LinuxCNC. Previously a docs-only build
silently omitted them.

Also adds homecomp.9 to COMP_MANPAGES alongside tpcomp.9 (both
.comp files are filtered out of COMPS because they do not compile
to .o modules, but their manpages are still worth shipping).
Surfaces in @hansu's review of #4081 as a
gen_complist: Broken link: ../man/man9/homecomp.9.html warning.

.9.adoc suffix matches the convention the docs HTML manpage rule
already expects under objects/man/.

Test plan

• Clean-tree make docs (English-only): 207 troff + 154 extracted
  component adocs, link checker clean.
• make ../docs/man/man9/homecomp.9 produces troff (was silently
  missing before).
• Standalone make ../docs/man/man9/abs.9 from a tree with no
  halcompile binary rebuilds halcompile and produces the manpage
  without touching C code.