docs(applicate): document v0.2 fork additions in READMEs/NOTICE/FORK_CHANGES

Update both READMEs, NOTICE.md, and FORK_CHANGES.md to describe the
v0.2.0-applicate fork additions: multi-document tabs with drag-reorder,
file drag-and-drop in reading and edit modes, session persistence,
fork-only About credit row, and the renderer fade-on-ready quick-fix.

FORK_CHANGES.md gets four new scope sections (Multi-Document Tabs,
Drag-and-Drop, About-Panel, Renderer Pipeline) so future contributors
see how the fork extends upstream without touching upstream files.

Author: applicate2628

FORK_CHANGES.md

@@ -40,6 +40,33 @@ This fork keeps upstream MarkMello source files unchanged. Fork-specific behavio
 - WebView mode has its own document minimap, scroll progress, width-resizer handle, and edit-preview rendering surface.
 - Native/WebView backend switching keeps the previous renderer visible until the target renderer is ready, then crossfades without a blank frame.
 
+## Multi-Document Tabs Scope
+
+- A fork-only tabs strip rendered above the document body shows every open document; each tab has a close-button and the active tab is visually distinct (brighter background, semibold label).
+- The strip lives in `src/MarkMello.Applicate.Desktop/Views/ApplicateTabsView.cs` as a code-only `UserControl`; it is mounted on top of `BodyPanel` at runtime by `ApplicateMainWindow` without modifying upstream XAML.
+- Document state is owned by `IOpenDocumentsService` (`src/MarkMello.Applicate.Desktop/Editing/`). The service is the single source of truth for the open document list and the active document; the upstream `MainWindowViewModel.Document` is mirrored from it via a bridge.
+- Tabs support click-to-activate, click-`×`-to-close (active-tab close routes through the upstream dirty prompt so cancel does not orphan the tab), and click+drag horizontal reorder with animated neighbour displacement.
+- Drag reorder uses Avalonia `TransformOperationsTransition` for neighbour tabs sliding into a new slot (160ms cubic ease-out); the dragged tab follows the cursor without transition so the press point stays anchored.
+- Open documents and the active tab are persisted between launches in JSON at `%AppData%/MarkMello/applicate-session.json` via `JsonApplicateSessionStore`.
+
+## Drag-and-Drop Scope
+
+- The Applicate WebView body and edit-preview surfaces accept file drag-and-drop without modifying upstream surfaces.
+- Reading-mode drops route through `IOpenDocumentsService.OpenAsync` and open the dropped file as a new tab; the service deduplicates by file content-hash so dropping the same file twice (or dropping a file that is already open) does not create a duplicate tab.
+- Edit-mode drops insert the file at the caret position. Image files are saved next to the document under `images/` with a content-hash collision suffix when a same-name image with different content already exists, and inserted as Markdown `![alt](images/name.png)` so the document remains portable.
+- Cross-source dedupe in the active-document bridge also catches files opened from different paths but with identical content and display name.
+
+## About-Panel Scope
+
+- Upstream `AppAboutPanelView` content is preserved unchanged. The fork swaps the popup's `Child` at runtime in `ApplicateMainWindow` to `ApplicateAppAboutPanelView`, which subclasses the upstream view and appends a second credit row underneath the upstream one.
+- The new row reads `Applicate additions by Dmitry Denisenko (applicate2628)` and links to the fork maintainer's GitHub profile. Upstream copyright notices remain visible per GPL-3.0 §5.
+- No upstream files are edited for the About panel; the override is contained in `src/MarkMello.Applicate.Desktop/Views/ApplicateAppAboutPanelView.cs`.
+
+## Renderer Pipeline Scope
+
+- The WebView renderer hides the document body, minimap, and width-resizer handle until the bootstrap pipeline finishes math + mermaid + code-block rendering and posts `layout-ready`. Without this gate the user briefly sees a fallback state on tab switch and fresh launch (web fonts not yet swapped, `\[ ... \]` math placeholders, raw mermaid source, width handle at a stale X coordinate). The reveal uses a 120ms CSS opacity transition shared by all three surfaces.
+- The hide-rule is scoped to `body > main.mm-document` (and the minimap aside, and the width-handle div) so that the minimap's cloned `.mm-document` subtree is not affected; the clone always renders at full opacity inside the minimap container.
+
 ## Packaging Scope
 
 - The upstream Windows installer remains in `packaging/windows/MarkMello.iss`.

NOTICE.md

@@ -33,6 +33,16 @@ Applicate additions are distributed under GPL-3.0 as part of this fork.
   and Wide presets.
 - Native and WebView minimap support for the Applicate viewer path.
 - Smooth Native/WebView renderer switching without a blank preview frame.
+- Multi-document tab strip above the body with click-to-activate, close-button
+  per tab, and drag-to-reorder with animated neighbor displacement.
+- Open-document and active-tab persistence across launches via a JSON session
+  store under `%AppData%/MarkMello/applicate-session.json`.
+- File drag-and-drop into the window: reading-mode drops open as new tabs,
+  edit-mode drops insert at the caret position with image files saved next
+  to the document and inserted as relative-link Markdown.
+- Fork-specific About panel credit row exposing this fork's authorship next
+  to the upstream credit, both rendered side by side without modifying the
+  upstream About view file.
 - Separate Windows installer metadata so the fork installs as `MarkMello Applicate`
   and does not reuse the upstream MarkMello AppId or ProgId.
 

README.en.md

@@ -26,7 +26,10 @@ Applicate additions:
 - keep the native renderer as a fallback and compatibility mode;
 - add flexible reader-width resizing by dragging the content edge while preserving the original Narrow, Medium, and Wide presets;
 - add a WebView minimap while preserving the native minimap for the native renderer;
-- keep reading, resize, theme, edit preview, and Native/WebView switching synchronized without a blank frame.
+- keep reading, resize, theme, edit preview, and Native/WebView switching synchronized without a blank frame;
+- add a tab strip above the document and a multi-document model: several `.md` files can be open at once, click a tab to switch, click `×` to close, drag a tab horizontally to reorder it within the strip;
+- remember the open document list and the active tab across launches (`%AppData%/MarkMello/applicate-session.json`);
+- accept file drag-and-drop in the window: in reading mode the dropped file opens as a new tab, in editing mode it is inserted at the caret position (images are saved next to the document and inserted as a relative link in the form `![](images/name.png)`).
 
 ## How it differs from regular Markdown editors
 

README.md

@@ -26,7 +26,10 @@ Applicate-добавления:
 - сохраняют native renderer как fallback и как режим совместимости;
 - добавляют гибкое изменение ширины чтения перетаскиванием края, сохраняя исходные пресеты Narrow, Medium и Wide;
 - добавляют minimap для WebView renderer и сохраняют native minimap для native renderer;
-- синхронизируют чтение, resize, theme, edit preview и переключение Native/WebView без пустого кадра.
+- синхронизируют чтение, resize, theme, edit preview и переключение Native/WebView без пустого кадра;
+- добавляют полосу вкладок над документом и multi-document модель: одновременно открыто несколько `.md` файлов, переключение кликом, закрытие крестиком, перетаскивание вкладок для смены порядка;
+- запоминают список открытых документов и активную вкладку между запусками (`%AppData%/MarkMello/applicate-session.json`);
+- принимают drag-and-drop файлов в окно: в режиме чтения — открытие как новой вкладки, в режиме редактирования — вставка в позицию каретки (изображения сохраняются рядом с документом и вставляются как относительная ссылка вида `![](images/name.png)`).
 
 ## Чем отличается от обычных Markdown-редакторов