chore: drop tracked output/ sample in favor of CI-built demo gallery (#4)

The dracula sample under output/dracula/ was a reference render for the
README. Now that demo/ auto-generates every card × every theme on each
push, the sample is redundant — and keeping it trackers means every
behavioral tweak shows up as a diff in committed SVGs.

- Delete output/dracula/*.svg.
- .gitignore: collapse `output/*` + `!output/dracula/` to a plain `output/`.
- demo.yml: drop `output/**` from paths-ignore (no longer part of any push).
- README / docs: point readers at demo/ instead of output/dracula/.

.github/workflows/demo.yml

@@ -5,7 +5,6 @@ on:
     branches: [main]
     paths-ignore:
       - "demo/**"
-      - "output/**"
       - "**.md"
       - "LICENSE"
   workflow_dispatch: