docs: add user docs for EffectCraft

Adds docs/user/ (published at getartcraft.com/docs/effectcraft), the docs-check
and docs-publish workflows (copied from craft-launcher), and a "User docs" rule
in AGENTS.md. Verified against 0.8.0.

Source notes per page:
- index: README, crates/engine/src/menus.rs, website crafting-apps.ts entry,
  docs/gaps.md (.aep).
- getting-started/install: README Downloads, gh release v0.8.0 assets,
  packaging/windows/effectcraft.wxs (per-machine, Start Menu, desktop shortcut
  box), package.ps1 (portable zip contents), launcher crates/core catalog.rs
  (EffectCraft listed), launcher docs install guide.
- guides/make-a-composition: menus.rs (Composition, Layer, Help), comp.rs
  shortcut, panels/comp_settings.rs (labels, presets, tabs), panels/home.rs,
  engine/src/learn.rs (Animate a title tutorial).
- guides/animate-with-keyframes: learn.rs, panels/timeline.rs (stopwatch, Add
  or remove keyframe), commands/prop.rs (Easy Ease F9), menus.rs (Animation).
- guides/add-an-effect: menus.rs (Effect, Window), panels/effects_presets.rs,
  commands/effect.rs, effects/src/misc.rs (Gaussian Blur parameters).
- guides/render-a-video: panels/render_queue.rs (labels), project
  render_queue.rs (format labels, default H.264, template, supports_alpha),
  commands/render_queue.rs (Cmd+M), README (Lottie).
- guides/import-footage: docs/footage.md, menus.rs, engine/src/prefs.rs
  (Sequence Footage), README (Wayland drop).
- troubleshooting/gpu-not-used: issues #596, #613; prefs.rs (Window Graphics),
  commands/app_more.rs (System Compatibility Report text), ui-egui menus.rs
  (GPU Information dialog text, checked at v0.8.0).
- troubleshooting/footage-missing: docs/footage.md (relink), commands/
  file_more.rs (Find Missing Footage), issue #652 and PR #676.
- faq/after-effects-projects: README "Where it stands", docs/gaps.md.
- faq/price-and-platforms: README (license, platforms, status), LICENSE files.

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

.github/workflows/docs-check.yml

@@ -0,0 +1,32 @@
+name: docs-check
+
+on:
+  pull_request:
+    paths: ["docs/user/**"]
+  push:
+    branches: [main]
+    paths: ["docs/user/**"]
+
+permissions:
+  contents: read
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+      - name: Download the shared docs checker
+        id: fetch
+        run: |
+          url=https://raw.githubusercontent.com/storytold/artcraft-services/main/frontend/apps/artcraft-website-next/scripts/docs/core.mjs
+          if curl -fsSL "$url" -o "$RUNNER_TEMP/docs-core.mjs"; then
+            echo "ok=1" >> "$GITHUB_OUTPUT"
+          else
+            echo "::warning::The docs checker is not published yet; skipping."
+          fi
+      - name: Check docs/user
+        if: steps.fetch.outputs.ok == '1'
+        run: node "$RUNNER_TEMP/docs-core.mjs" docs/user