Remove the baked-in announcement (rely on the live feed)

The app no longer ships a built-in announcement — announcements come only from
the live basisvr.org/announcements.json feed. The embedded fallback is now empty,
so offline the app shows nothing rather than a stale baked-in notice. Seen-tracking
is unchanged: SeenAnnouncementIds still records read announcements so they don't
re-badge as unread.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: dooly123

src/BasisPM.Core/announcements.json

@@ -1,12 +1 @@
-[
-  {
-    "id": "2026-07-04-early-preview",
-    "level": "info",
-    "pinned": true,
-    "date": "2026-07-04",
-    "title": "This is a preview — and still very early",
-    "body": "Thanks for trying the Basis Package Manager! It's an early preview and very much a work in progress, so expect rough edges, missing features, and the occasional breaking change. Your feedback genuinely shapes where it goes next.",
-    "url": "https://discord.gg/v6ve6WT562",
-    "linkText": "Share feedback on Discord"
-  }
-]
+[]

tests/BasisPM.Core.Tests/AnnouncementServiceTests.cs

@@ -7,11 +7,10 @@ namespace BasisPM.Core.Tests;
 public sealed class AnnouncementServiceTests
 {
     [Fact]
-    public void LoadEmbedded_returns_the_baked_in_feed()
+    public void LoadEmbedded_returns_an_empty_feed()
     {
-        var items = AnnouncementService.LoadEmbedded();
-        Assert.NotEmpty(items);
-        Assert.Contains(items, a => a.Id == "2026-07-04-early-preview" && a.Pinned);
+        // No announcements are baked into the app — they come only from the live feed.
+        Assert.Empty(AnnouncementService.LoadEmbedded());
     }
 
     [Fact]
@@ -66,8 +65,9 @@ public async Task LoadAsync_sorts_undated_items_last()
     [Fact]
     public async Task LoadAsync_falls_back_to_embedded_when_offline()
     {
+        // Offline falls back to the embedded feed, which is now empty (no baked-in announcements).
         var svc = new AnnouncementService(StubHttpMessageHandler.AlwaysThrows());
         var items = await svc.LoadAsync("https://example.com/announcements.json");
-        Assert.Contains(items, a => a.Id == "2026-07-04-early-preview");
+        Assert.Empty(items);
     }
 }