feat: client and server logic to manage announcements (#3)

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### Tests

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Reviewed-on: #3
Co-authored-by: Naomi Carrigan <commits@nhcarrigan.com>
Co-committed-by: Naomi Carrigan <commits@nhcarrigan.com>

client/package.json

@@ -28,6 +28,7 @@
     "@angular/forms": "20.0.6",
     "@angular/platform-browser": "20.0.6",
     "@angular/router": "20.0.6",
+    "ngx-markdown": "20.0.0",
     "rxjs": "7.8.2",
     "tslib": "2.8.1",
     "zone.js": "0.15.1"