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>

tsconfig.json

@@ -0,0 +1,28 @@
+{
+  "compileOnSave": false,
+  "compilerOptions": {
+    "outDir": "./dist/out-tsc",
+    "strict": true,
+    "noImplicitOverride": true,
+    "noPropertyAccessFromIndexSignature": true,
+    "noImplicitReturns": true,
+    "noFallthroughCasesInSwitch": true,
+    "skipLibCheck": true,
+    "esModuleInterop": true,
+    "sourceMap": true,
+    "declaration": true,
+    "experimentalDecorators": true,
+    "moduleResolution": "bundler",
+    "importHelpers": true,
+    "target": "ES2022",
+    "module": "ES2022",
+    "lib": ["ES2022", "dom"],
+    "useDefineForClassFields": false
+  },
+  "angularCompilerOptions": {
+    "enableI18nLegacyMessageIdFormat": false,
+    "strictInjectionParameters": true,
+    "strictInputAccessModifiers": true,
+    "strictTemplates": true
+  }
+}