chore: unify footer across pages; switch license to PolyForm-NC

.github/dependabot.yml

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+# Dependabot — only watches GitHub Actions versions.
+# This repo has no runtime dependencies (no package.json, no requirements.txt).
+# The site is static HTML/CSS/JS served from main.
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: monthly
+    open-pull-requests-limit: 5
+    commit-message:
+      prefix: chore
+      include: scope

.github/workflows/checks.yml

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+# Site checks — link validity + HTML sanity on every PR and main push.
+# This repo has no build step. Static HTML/CSS/JS is what ships to
+# GitHub Pages from `main`. CI here just guards against shipping
+# broken links or malformed HTML.
+name: site-checks
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+# Cancel in-progress runs for the same branch when a new commit lands.
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  links:
+    name: link checker
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      # lychee is a fast link checker — supports HTML, markdown, and
+      # ignores false positives via a config file when one is added.
+      - name: Check links
+        uses: lycheeverse/lychee-action@v2
+        with:
+          # Config lives in lychee.toml at repo root: accept-codes,
+          # excludes for sites with known SSL/UA quirks, root-dir for
+          # root-relative href resolution.
+          args: >-
+            --no-progress
+            --config lychee.toml
+            --root-dir ${{ github.workspace }}
+            ./index.html
+            ./data/index.html
+            ./inequality/index.html
+            ./spend/index.html
+            ./README.md
+            ./SECURITY.md
+            ./CONTRIBUTING.md
+          fail: true
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
+  html:
+    name: html validation
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      # html-validate is a fast standalone HTML5 validator — no DOM,
+      # no headless browser. Catches structural issues only.
+      - name: Set up Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+      - name: Install html-validate
+        run: npm install --no-save html-validate@9
+      - name: Validate HTML
+        run: |
+          npx html-validate \
+            --formatter codeframe \
+            index.html \
+            data/index.html \
+            inequality/index.html \
+            spend/index.html

.htmlvalidate.json

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+{
+  "extends": ["html-validate:recommended"],
+  "rules": {
+    "void-style": "off",
+    "no-trailing-whitespace": "off",
+    "no-inline-style": "off",
+    "wcag/h32": "off",
+    "wcag/h67": "off",
+    "no-redundant-role": "off",
+    "no-redundant-aria-label": "off",
+    "long-title": "off",
+    "attribute-boolean-style": "off",
+    "no-implicit-button-type": "off",
+    "valid-id": "off",
+    "no-raw-characters": "off",
+    "unrecognized-char-ref": "off",
+    "prefer-native-element": "off",
+    "element-permitted-content": "off",
+    "aria-label-misuse": "off"
+  }
+}