test: semantic package lint, LO style resolution, cross-format rendering

Three legs against the closed-loop blind spot the duplicate-style bug
exposed: package-lint.test.ts checks invariants the schemas cannot
express (unique style ids/names, dangling style/num/rel references,
balanced ranges, manifest completeness); lo-roundtrip gains a
soffice→fodt leg asserting the styles LibreOffice resolves (Heading
chain Arial/bold/sizes, Word defaults); lo-render-consistency.test.ts
renders the kitchen sink from both formats through LibreOffice and
compares pagination and pixels (ratchet thresholds). CI's LO job
gains poppler-utils; test:lo runs both LO files.

.github/workflows/ci.yml

@@ -39,7 +39,8 @@ jobs:
         with:
           node-version: 20
           cache: npm
-      - run: sudo apt-get update && sudo apt-get install -y --no-install-recommends libreoffice-writer fonts-liberation
+      # poppler-utils rasterizes the PDFs the render-consistency leg compares.
+      - run: sudo apt-get update && sudo apt-get install -y --no-install-recommends libreoffice-writer fonts-liberation poppler-utils
       - run: npm ci
       - run: npm run test:lo