Port framework improvements from backend and split into eleven packages

[KRSogaard]

MagicCSharp was extracted from the backend in June and the two diverged; every shared file differed. This brings the backend's improvements across and splits the packages so a consumer takes only what it uses.

Packages
Six new: AspNetCore, Scheduling, Data.EntityFramework, Data.Postgres, Testing and Testing.Database. Core drops from six dependencies to three and no longer pulls in ASP.NET Core or distributed locking; Data no longer pulls in Entity Framework, so a domain project can reference the repository interfaces without taking on a persistence library; Testing has no xUnit or Testcontainers, so wanting FakeClock does not mean wanting Docker.

Data
One IRepository<TEntity, TKey, TEdit, TFilter> replaces the two interfaces that hardcoded long. Soft delete, pagination and search become opt-in interfaces with base classes for both key shapes. Adds GetKeys, batch update by dictionary and by list, delete by filter, untracked reads, and the re-read after write that populates navigation properties.

MagicDbContext stores enums by name (including inside JSON columns) so inserting an enum member no longer changes what existing rows mean, and normalizes timestamps to UTC. The Postgres package adds a pooled context factory that fails at startup on a bad connection string, a design-time factory for dotnet ef, and a command interceptor covering the query predicates and ExecuteUpdate/Delete that never reach SaveChanges.

Testing
New. A clock you move by hand, ids derived from it, an event dispatcher that runs handlers inline so assertions need no sleeping, a re-entrant in-memory lock, and a base class for repository tests against real PostgreSQL in Testcontainers.

Fixes

• AddMagicUseCases picked implementations with FirstOrDefault, so two implementations meant one was chosen silently by reflection order. Now throws and names both.
• The same scan only saw already-loaded assemblies, so use cases in an untouched project were never registered.
• LocalEventDispatcher blocked while Kafka and SQS are fire-and-forget, so a handler re-entering its emitter's lock worked locally and deadlocked in production.
• ScheduledBackgroundService logged its next run from the wall clock while scheduling from the injected IClock.
• Core pinned Microsoft.AspNetCore.Http.Abstractions 2.2.0.

Tooling
tools/ holds AddEntity, ValidateConventions and SyncAllProjects as single-file programs, keyed off magiccsharp.json rather than hardcoded paths so they work in any repository using the layout.

Tests
47, where there were none.

Libraries stay on net9.0 so net9 and net10 apps can both consume them. See CHANGELOG.md for the full list and the migration guide.