feat: initial rich-text-elements-ui library implementation

TipTap-powered rich text editing library with WYSIWYG editor, markdown editor,
template editor, collaboration support (Yjs), mentions, track changes,
comments, code blocks, and table insertion.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ng-package.json

@@ -0,0 +1,40 @@
+{
+  "$schema": "node_modules/ng-packagr/ng-package.schema.json",
+  "lib": {
+    "entryFile": "src/index.ts",
+    "styleIncludePaths": ["src/styles"]
+  },
+  "dest": "dist",
+  "deleteDestPath": true,
+  "assets": [
+    "src/styles/**/*.scss"
+  ],
+  "allowedNonPeerDependencies": [
+    "@tiptap/core",
+    "@tiptap/starter-kit",
+    "@tiptap/pm",
+    "@tiptap/extension-placeholder",
+    "@tiptap/extension-character-count",
+    "@tiptap/extension-color",
+    "@tiptap/extension-text-style",
+    "@tiptap/extension-highlight",
+    "@tiptap/extension-link",
+    "@tiptap/extension-image",
+    "@tiptap/extension-table",
+    "@tiptap/extension-table-row",
+    "@tiptap/extension-table-cell",
+    "@tiptap/extension-table-header",
+    "@tiptap/extension-task-list",
+    "@tiptap/extension-task-item",
+    "@tiptap/extension-underline",
+    "@tiptap/extension-text-align",
+    "@tiptap/extension-subscript",
+    "@tiptap/extension-superscript",
+    "@tiptap/extension-mention",
+    "@tiptap/extension-code-block-lowlight",
+    "@tiptap/extension-bubble-menu",
+    "@tiptap/extension-floating-menu",
+    "lowlight",
+    "marked"
+  ]
+}