refactor(tags): remove tag entity and all references

Drops TagEntity, TagRepository, and tag wiring across data layer, worker,
and UI. Adds RemoveTags migration to clean up schema.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ClaudeDo.Ui/Services/WorkerClient.cs

@@ -395,23 +395,6 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
         await _hub.InvokeAsync("SetTaskStatus", taskId, status.ToString());
     }
 
-    public async Task SetTaskTagsAsync(string taskId, IEnumerable<string> tagNames)
-    {
-        await _hub.InvokeAsync("SetTaskTags", taskId, tagNames.ToArray());
-    }
-
-    public async Task<List<string>> GetAllTagsAsync()
-    {
-        try
-        {
-            return await _hub.InvokeAsync<List<string>>("GetAllTags") ?? new List<string>();
-        }
-        catch
-        {
-            return new List<string>();
-        }
-    }
-
     public async Task<WorktreeCleanupDto?> CleanupFinishedWorktreesAsync()
     {
         try