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

Musify.Application/Configuration/UploadIntentConfiguration.cs

@@ -0,0 +1,42 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Musify.Application.Configuration
+{
+    public class UploadIntentConfiguration
+    {
+        public const string SectionName = "UploadIntent";
+
+        [Range(10, 3600)]
+        public int UploadUrlExpiresInSeconds { get; set; } = 120;
+
+        [Range(1, 100)]
+        public int MaxActiveUploadIntentsPerUser { get; set; } = 5;
+
+        [Range(1, long.MaxValue)]
+        public long MaxActiveUploadBytesPerUser { get; set; } = 200L * 1024 * 1024;
+
+        [Range(1, long.MaxValue)]
+        public long MaxUploadBytes { get; set; } = 100L * 1024 * 1024;
+
+        [Range(1, long.MaxValue)]
+        public long DefaultExpectedPictureSizeBytes { get; set; } = 10L * 1024 * 1024;
+
+        [Range(1, long.MaxValue)]
+        public long DefaultExpectedAudioSizeBytes { get; set; } = 100L * 1024 * 1024;
+
+        [Range(30, 86400)]
+        public int ExpirationJobIntervalSeconds { get; set; } = 300;
+
+        [Range(0, 365)]
+        public int ExpiredIntentsRetentionDays { get; set; } = 7;
+
+        [Required, MinLength(1)]
+        public string TemporalRootPrefix { get; set; } = "temporal";
+
+        [Range(1, 30)]
+        public int TemporalUploadsRetentionDays { get; set; } = 3;
+
+        [Range(60, 86400)]
+        public int TemporalCleanUpJobIntervalSeconds { get; set; } = 3600;
+    }
+}