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

every object with an .image record should now carry the images
flag.

Previously DocObj_Has_.images was read but never written anywhere
in the tree, so no object carried it: .ssp emitted has_images = 0
for every object of every document.

(assisted by Claude-Code)

Complete image file digest identity record: add
px:<width>x<height> to the .ssp image record, read from the
image file header (imageformats.read_image_info, no decode):

  .image: won_benkler_2_1.png sha256:5BA4...D128 bytes:93861 px:420x342

(The w##h## dimensions in the markup are display dimensions, not the
file's: they are author set, or where given as w0h0 are derived by
_image_dimensions and capped to a maximum display width, and they
become the width/height attributes of the output format image display).

(assisted by Claude-Code)

Modules and imports rewritten to sisudoc.ocda.* and
sisudoc.outputs.*; dub.json excludedSourceFiles and the
spine:abstraction sub-package sourcePaths collapsed to
./src/sisudoc/ocda.

Verified: nix build .#spine-overlay-ldc clean.

(assisted by Claude-Code)

create new directories under ./src/sisudoc ocda & outputs in order to
separate the document abstraction library from downstream output
processing (stuff broken till paths & modules fixed)