docs: add backend diff-vs-main + sales guide, document editor motion & HTML editor

- docs/BACKEND-DIFF-VS-MAIN.md: backend handoff summary framing BACKEND.md
- docs/SALES-GUIDE.md: non-technical demo/enablement guide
- docs/EDITOR.md: document interaction/motion pass and HTML editor status

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/EDITOR.md

@@ -69,6 +69,22 @@ All 11 section components (`sections/*.component.html`) share these 6 `shared/ui
 
 `section.shared.scss`'s `.editor-grid.*` classes are unchanged and still used inside `SectionCard` bodies; only the outer `.editor-section-card` shell and per-section `<h2>` were replaced (that rule has been removed from the shared stylesheet since it has no remaining consumers).
 
+## Interaction / motion pass (2026-07-16)
+
+Interaction feedback + motion applied consistently, all gated behind `prefers-reduced-motion`:
+
+- `section.shared.scss` `button`/`button.secondary` gained hover/active/`focus-visible`/`disabled` states (previously flat, no feedback across all 11 sections).
+- `project-editor-page.component.scss`: the active section fades/slides in (220ms) when the `@switch` swaps components; the "reset section" button got matching hover/focus states.
+- `project-editor-save-bar` buttons now use the shared `app-button` primitive (danger / secondary / primary variants) instead of unstyled native `<button>`s.
+
+## HTML editor (Static Pages)
+
+`MarketplaceHtmlEditorComponent` (`components/html-editor/marketplace-html-editor.component.ts`) is a `contenteditable` WYSIWYG used inside the Static Pages editor (`features/content-management/.../static-pages-editor.component.html`), one instance per locale, bound `[html]` / `(htmlChange)`.
+
+**Status: working.** Verified live 2026-07-16 — typing captured, toolbar commands functional (bold toggles, `insertUnorderedList` wraps `<ul><li>`, H2/H3/link/image/table), `htmlChange` emits on every edit, and a "Код" toggle swaps to raw-HTML editing.
+
+**Caveat:** implemented on the deprecated `document.execCommand` API. It works in all current browsers today but is a legacy web API with no modern drop-in replacement; if a future browser drops it, this component needs a rewrite (e.g. a maintained rich-text library). By design it emits **raw, unsanitized** HTML — sanitization is a storefront-render concern, not an authoring one (see `docs/BACKEND.md` item 4 on server-side content moderation on publish).
+
 ## Field-description / dropdown UX (Sprint 19+)
 
 Every field across the 10 editor section templates now carries a one-line, i18n'd description under its label explaining what it does in plain language (all new copy routed through `TranslateService`/`TranslatePipe`, added to `Translations` + `en.ts`/`ru.ts`/`hy.ts` following the existing `builder.*` key pattern — see `src/app/i18n/translations.ts`).