ocda: fixed inverted object_number_off on body paragraphs

ssp: make use of curly braces (code-style)

(assisted by Claude-Code)

--+# clears dummy_heading_multiple_objects, fixed

until fix, following any ---# ... --+# block every ~# object in
the document was marked dummy_heading, (and the output generators
that honour that flag suppressed its text: so ~# behaved as -#.
One line added to correct the --+# branch.

~# suppresses the object's number only, content is still shown.
-# is for a heading introduced solely to segment an output:
object number suppressed and the heading text omitted from the
body where the output format allows, the toc entry kept. Both were
already correct in isolation; only the leaked block flag broke ~#.

(assisted by Claude-Code)

sisu-spine-markup.sst needs review and update, it was taken from
the much older sisu (ruby) writing and was itself a part of a more
comprehensive document (sisu-manual). Some updates.

(assisted by Claude-Code)

fix to --abstraction/.ssp: fix document structure, representation
parent, ancestors, children. Make parent_ocn, the marked-up and
collapsed ancestor arrays, and the children correctly represent
the document structure. fixed

(assisted by Claude-Code)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01836BxBb8LvVKJ8sBg7Dx6U

for document abstraction and its .ssp output, removed the
requirement of including --abstraction & --serial flags to produce
correct output (for: .dom_status, .dom_status_collapsed &
.last_descendant)

- meta_processing_xml_dom() includes show_abstraction, so --pod2
  and --show-abstraction run the dom pass; last_descendant is
  derived from that pass via after_doc_get_descendants()

The accumulators are now verified as eight wide locals of
docAbstraction(), so each document starts clean and no two threads
share one.
- bug: the four dom accumulators were template scope (shared) and
  nine wide, while their end of document reset was eight wide, so
  the first document of a run differed from the rest and parallel
  runs raced on one buffer, (which also mis-nested epub toc_nav)

test/ reference .ssp regenerated: accelerando only, trailing zero
dropped.
test-abstraction-ssp.sh now runs parallel and diffs output against
a serial run.

(assisted by Claude-Code)

- dmd 2.112.1
- ldc 1.43.0 beta1
- dub 1.41.0
- dtools 2.112.1