Initial commit: notification-elements-ui library

Angular 19 component library for notifications & communication:
- ntf-bell: notification bell with badge count and shake animation
- ntf-feed / ntf-feed-item: real-time notification feed with grouping
- ntf-center: full notification center with category filter tabs
- ntf-inbox / ntf-inbox-item: two-column inbox with search and detail
- ntf-comment / ntf-thread: comment threads with replies and reactions
- ntf-mention-input: text input with @mention autocomplete
- ntf-empty-state: empty state placeholder
- ntf-item-def: custom template directive for notification items

Includes signal-based services, SCSS design tokens with dark mode,
utility functions, and full TypeScript type definitions.

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

ng-package.json

@@ -0,0 +1,12 @@
+{
+  "$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"
+  ]
+}