0.10: Add DI, hosting, and explicit unit-of-work support

[bazer]

Objective

Make DataLinq a deliberate, lifetime-safe component of ASP.NET Core and Generic Host applications through an explicit host-integration package, injectable read access, and an explicit mutable unit-of-work boundary.

Required scope

• Define a host-integration package boundary without imposing an ASP.NET Core dependency on the core runtime.
• Register generated database models and current providers with validated options.
• Separate injectable read access from explicit mutable unit-of-work ownership.
• Add a unit-of-work factory whose instances own transaction begin, commit, rollback, cancellation, disposal, and terminal-state reporting.
• Document singleton/scoped/transient ownership for provider state, generated roots, connections, transactions, units of work, and hosted services.
• Integrate with Generic Host logging.
• Preserve existing SQL mutable-instance trust rules across failed commit, cancellation, rollback failure, and disposal.
• Make shutdown and disposal deterministic and exactly once.

Acceptance criteria

• ASP.NET Core and worker-style Generic Host fixtures resolve read services and execute one explicit unit of work.
• Concurrent scopes cannot accidentally share transaction or mutable unit-of-work state.
• Begin, commit, rollback, cancellation, failure, uncertain outcome, and disposal paths have focused contract tests.
• Nested application services can participate through explicit ownership without an ambient session.
• Host shutdown disposes every owned resource exactly once.
• New packages are included in central versioning, pack inventory, package inspection, compatibility checks, and consumer smoke without leaking unnecessary dependencies.
• Focused H10 evidence is recorded in 0.10: Produce release evidence and frozen-candidate closeout #106 before this issue closes.

Dependency and order

• Blocked on the stable public async/cancellation surface from 0.10: Implement native async and cancellation #107.
• Package scaffolding may begin earlier, but public lifetimes cannot freeze until 0.10: Implement native async and cancellation #107's W3 contract is stable.
• This issue blocks final startup-validation host integration and the fake-unit-of-work/DI portion of T10.

Explicit non-goals

• Implicit ambient transactions or an AsyncLocal session.
• Automatic transactions for ordinary reads.
• Automatic migrations at startup.
• Named or keyed database registrations in 0.10.
• Framework-specific XAML packages.

Planning sources

• 0.10 H10 roadmap contract
• Implementation order W4
• Durable hosting design plan