Migrate Breweries to a vertical slice (Features.Breweries)

Moves brewery CRUD from the Service.Breweries/Infrastructure.Repository
layered split into a single Features.Breweries project: MediatR
commands/queries replace BreweryService, and the repository moves in
alongside its own controller. Extracts Infrastructure.Sql out of
Infrastructure.Repository (just the generic ADO.NET connection/base-repo
plumbing) since Breweries no longer needs the rest of that project, while
Auth and UserAccount repos still do until their own migration.

Also fixes the API.Core and Infrastructure.Repository.Tests Dockerfiles,
which were restoring against COPY destinations that didn't match the
projects' actual relative paths (silently working only because of the
COPY . . that followed); both now restore against Core.slnx with correctly
nested paths, verified with a real docker build.

web/backend/Infrastructure/Infrastructure.Sql/ISqlConnectionFactory.cs

@@ -0,0 +1,15 @@
+using System.Data.Common;
+
+namespace Infrastructure.Sql;
+
+/// <summary>
+/// Factory for creating database connections used by repositories.
+/// </summary>
+public interface ISqlConnectionFactory
+{
+    /// <summary>
+    /// Creates a new, unopened database connection.
+    /// </summary>
+    /// <returns>A new <see cref="DbConnection"/> instance.</returns>
+    DbConnection CreateConnection();
+}