feat(skill): add documents family skill (PDF / Word / Excel / PowerPoint) (#262)

* feat(skill): add documents family skill (PDF / Word / Excel / PowerPoint)

One family skill for PDF, Word (.docx), Excel (.xlsx), and PowerPoint
(.pptx) per the family-skill rule (epub precedent): shared workflow in
SKILL.md (scope, content model, template, render, validate, deliver) with
per-format load-on-demand references, generation templates per format, a
stdlib validation script (--json, structural sanity + render check with
graceful degradation), one fixture per format, a unittest suite, six
output-quality eval cases spanning all four formats, a human README, the
README.md index entry, and regenerated catalogs.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

* fix(skill): dispatch PDF renderer args per binary in documents validation

The render check passed pdftoppm-only flags (-png/-r/-f/-l) to mutool and
ghostscript, which reject them, so a machine with only mutool or gs would
false-FAIL valid PDFs. Dispatch per-renderer argument sets (pdftoppm -png;
mutool draw -o; gs -sDEVICE=png16m) and cover the dispatch with a unit test.
Also: count PDF pages via the /Count page-tree fallback (page objects can
hide in compressed ObjStm streams), drop the stale "unsupported input" exit-2
claim from the docstring, and stop labeling skipped files with a FAIL check.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

* style(skill): drop redundant local tempfile import in renderer dispatch test

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

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Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

.codex-plugin/plugin.json

@@ -52,6 +52,7 @@
     "./data-scientist",
     "./de-spin",
     "./docker-compose",
+    "./documents",
     "./dspy",
     "./epub",
     "./esp32-development",