docs: add user docs for DesignCraft

Baseline user docs in docs/user/ (published at getartcraft.com/docs/designcraft),
the docs-check and docs-publish workflows, and a "User docs" rule in AGENTS.md.

Source notes per page:
- index.md: README (intro, features, license), website crafting-apps.ts entry.
- getting-started/index.md: crates/ui-egui/src/chrome.rs start_screen buttons.
- getting-started/install.md: README Downloads, gh release view v0.6.0 asset list,
  packaging/windows/designcraft.wxs (Start Menu shortcut), launcher catalog.rs.
- guides/create-a-document.md: dialogs.rs newDocument dialog, build.rs PRESETS,
  menus.rs UI_COMMANDS, chrome.rs start screen.
- guides/open-a-file.md: apps/designcraft main.rs open_filters, engine file.rs and
  interchange.rs docs, lib.rs import warnings test, issue #110.
- guides/place-images-and-text.md: main.rs place filters, engine file.rs file.place,
  dialogs.rs pdfImport, menus.rs placeWithOptions, release notes (#80).
- guides/export-a-pdf.md: dialogs.rs pdf_export and apply_pdf_preset, menus.rs.
- troubleshooting/app-closes-at-start.md: README graphics backend and logs,
  apps/designcraft/src/gpu.rs, issues #167, #192, #220, #273.
- troubleshooting/get-help.md: README Logs section.
- faq/is-it-free.md: README, docs/gaps.md. faq/supported-systems.md: README,
  release assets. faq/indesign-files.md: main.rs open filters, issues #450, #451, #110.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.github/workflows/docs-publish.yml

@@ -0,0 +1,22 @@
+name: docs-publish
+
+on:
+  push:
+    branches: [main]
+    paths: ["docs/user/**"]
+
+permissions: {}
+
+jobs:
+  rebuild:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Rebuild getartcraft.com
+        env:
+          HOOK: ${{ secrets.DOCS_BUILD_HOOK }}
+        run: |
+          if [ -z "$HOOK" ]; then
+            echo "DOCS_BUILD_HOOK is not set; the nightly website build will pick this up."
+            exit 0
+          fi
+          curl -fsS -X POST -d '{}' "$HOOK?trigger_title=docs%20update%20from%20$GITHUB_REPOSITORY"