refactor: standardize project names to Musify.* and flatten layout

- Flatten nested per-repo folders into flat Musify.* projects at root
- Rename assemblies/csproj: Domain->Musify.Domain, Application->Musify.Application,
  Infrastructure->Musify.Infrastructure, WebApi->Musify.Api, Worker->Musify.Worker,
  StreamingGateway->Musify.StreamingGateway
- Rename WebApi.* namespaces to Musify.Api.*
- Update all ProjectReference paths and the solution file
- Consolidate stray per-repo dotfiles; add root .gitattributes
- Move flutter client out to _archive

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Musify.Api/Authentication/JwtBearerOptionsSetup.cs

@@ -0,0 +1,37 @@
+using Microsoft.AspNetCore.Authentication.JwtBearer;
+using Microsoft.Extensions.Options;
+using Microsoft.IdentityModel.Tokens;
+using System.Security.Claims;
+
+namespace Musify.Api.Authentication;
+
+public sealed class JwtBearerOptionsSetup(IOptions<AuthenticationConfiguration> options)
+    : IConfigureNamedOptions<JwtBearerOptions>
+{
+    private readonly AuthenticationConfiguration _configuration = options.Value;
+
+    public void Configure(string? name, JwtBearerOptions options)
+    {
+        if (name != JwtBearerDefaults.AuthenticationScheme)
+        {
+            return;
+        }
+
+        Configure(options);
+    }
+
+    public void Configure(JwtBearerOptions options)
+    {
+        options.MetadataAddress = _configuration.MetadataAddress;
+        options.RequireHttpsMetadata = _configuration.RequireHttpsMetadata;
+        options.Audience = _configuration.AudienceAddress;
+        options.TokenValidationParameters = new TokenValidationParameters
+        {
+            ValidIssuer = _configuration.IssuerAddress,
+            ValidAudience = _configuration.AudienceAddress,
+            RoleClaimType = ClaimTypes.Role,
+            NameClaimType = ClaimTypes.Name,
+        };
+        options.EventsType = typeof(JwtBearerEventsHandler);
+    }
+}