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>

package.json

@@ -0,0 +1,39 @@
+{
+  "name": "@sda/notification-elements-ui",
+  "version": "0.1.0",
+  "description": "Angular components for notification center, real-time feeds, inbox, comment threads, and @mentions powered by @sda/base-ui",
+  "keywords": [
+    "angular",
+    "notifications",
+    "inbox",
+    "comments",
+    "mentions",
+    "feed",
+    "components",
+    "ui"
+  ],
+  "repository": {
+    "type": "git",
+    "url": "https://git.sky-ai.com/ui-core-design/notification-elements-ui.git"
+  },
+  "license": "MIT",
+  "sideEffects": false,
+  "scripts": {
+    "build": "ng-packagr -p ng-package.json",
+    "build:dev": "./build-for-dev.sh"
+  },
+  "peerDependencies": {
+    "@angular/common": "^19.0.0",
+    "@angular/core": "^19.0.0",
+    "@sda/base-ui": "*"
+  },
+  "devDependencies": {
+    "@angular/common": "^19.1.0",
+    "@angular/compiler": "^19.1.0",
+    "@angular/compiler-cli": "^19.1.0",
+    "@angular/core": "^19.1.0",
+    "@angular/forms": "^19.2.18",
+    "ng-packagr": "^19.1.0",
+    "typescript": "~5.7.2"
+  }
+}