Document IConfigureMarten + DI as the path for modular projection registration (#4326)

[jeremydmiller]

Summary

Closes #4326.

The issue asked for a module-aware AddProjectionWithServices overload that could be reached from inside an IConfigureMarten. Per the maintainer's reply on the issue:

If you're registering an IConfigureMarten, you can poke whatever dependencies you want through the constructor function.

This is correct — IConfigureMarten implementations are resolved by the host's IoC container, so the constructor is already a DI seam. A module just needs to take the projection's dependencies through its IConfigureMarten constructor and register the projection inside Configure(...). The docs didn't make that path explicit, which is what this PR addresses.

What changes

• New ProductProjectionRegistration : IConfigureMarten next to the existing ProductProjection sample. Takes IPriceLookup through the constructor, builds a ProductProjection, registers it on StoreOptions.
• New AddProductModule extension method demonstrating the module shape (wires both the IPriceLookup and the IConfigureMarten in one call).
• New use_iconfiguremarten_module_to_register_di_aware_projection integration test exercising the path end-to-end — host registers the module, an event is appended, and the projection populates Price via the injected dependency.
• New "Registering DI-aware projections through IConfigureMarten modules" section in docs/events/projections/ioc.md, sourced from the new sample regions. Includes a tip that the same pattern works for subscriptions and IConfigureMarten<TStore>, plus a "When to use which" table contrasting the IConfigureMarten path with AddProjectionWithServices.

Test plan

• use_iconfiguremarten_module_to_register_di_aware_projection passes on net10.0 against the ioc_module schema; the assertion that product.Price > 0 proves IPriceLookup reached the projection through the IConfigureMarten constructor.
• npm run docs renders the new section, the two <!-- snippet: ... --> blocks resolve to the new #regions in projections_with_IoC_services.cs, and the cross-link to /configuration/hostbuilder#composite-configuration-with-configuremarten resolves.

🤖 Generated with Claude Code