docs: the repository of its own: licences, CI, citations checked in form (P13 step 6)

spec/ and examples/ are CC BY 4.0, the code MIT OR Apache-2.0. The
verbatim-pin and rules.md-id checks need wanderbooks' vendored sources and
rules.md, so they move to wanderbooks; here a citation is checked in form.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

.github/workflows/check.yml

@@ -0,0 +1,32 @@
+# Every change: format, clippy and rustdoc with zero warnings, every test.
+# The two GnuCash tests need Docker and stay ignored here.
+name: check
+on:
+  push:
+  pull_request:
+concurrency:
+  group: check-${{ github.ref }}
+  cancel-in-progress: true
+jobs:
+  check:
+    runs-on: ubuntu-24.04
+    env:
+      CARGO_INCREMENTAL: "0"
+      CARGO_PROFILE_DEV_DEBUG: line-tables-only
+      CARGO_PROFILE_TEST_DEBUG: line-tables-only
+    steps:
+      - uses: actions/checkout@v4
+      - name: Room for the build (the image ships toolchains we never use)
+        run: |
+          sudo rm -rf /usr/share/dotnet /usr/local/lib/android /opt/ghc \
+                      /opt/hostedtoolcache/CodeQL /usr/local/.ghcup
+          df -h / | tail -1
+      - run: cargo fmt --all --check
+      - run: cargo clippy --workspace --all-targets -- -D warnings
+      - run: cargo doc --workspace --no-deps --quiet
+        env:
+          RUSTDOCFLAGS: -D warnings
+      - run: cargo test --workspace
+      - name: What the build used
+        if: always()
+        run: df -h / | tail -1