feat(CUB-28): [Extrudex] Define filament inventory database entities

Add storage_location and is_archived fields to Spool entity to complete
the filament inventory entity definition per CUB-28 requirements.

Changes:
- Spool entity: add IsArchived (bool, default false) and StorageLocation
  (nullable string, max 200) for physical inventory tracking
- SpoolConfiguration: add snake_case column mappings, defaults, and indexes
  (ix_spools_is_archived, ix_spools_active_archived composite)
- FilamentDtos: add IsArchived + StorageLocation to Response, Create, Update
- FilamentQueryDtos: add IncludeArchived and StorageLocation query filters
- FilamentsController: wire new fields into query, create, update, mapping
- FilamentValidators: add StorageLocation max-length validation

Build: PASS (0 errors)

backend/Infrastructure/Data/Configurations/SpoolConfiguration.cs

@@ -68,6 +68,15 @@ public class SpoolConfiguration : BaseEntityConfiguration<Spool>
             .HasDefaultValue(true)
             .IsRequired();
 
+        builder.Property(e => e.IsArchived)
+            .HasColumnName("is_archived")
+            .HasDefaultValue(false)
+            .IsRequired();
+
+        builder.Property(e => e.StorageLocation)
+            .HasColumnName("storage_location")
+            .HasMaxLength(200);
+
         // Unique index on spool_serial — critical for barcode/QR scanning
         builder.HasIndex(e => e.SpoolSerial)
             .IsUnique()
@@ -89,6 +98,14 @@ public class SpoolConfiguration : BaseEntityConfiguration<Spool>
         builder.HasIndex(e => e.IsActive)
             .HasDatabaseName("ix_spools_is_active");
 
+        // Index on is_archived for inventory filtering (exclude archived from default views)
+        builder.HasIndex(e => e.IsArchived)
+            .HasDatabaseName("ix_spools_is_archived");
+
+        // Composite index on is_active + is_archived for common inventory queries
+        builder.HasIndex(e => new { e.IsActive, e.IsArchived })
+            .HasDatabaseName("ix_spools_active_archived");
+
         // Relationships
         builder.HasOne(e => e.MaterialBase)
             .WithMany(e => e.Spools)