Licence: modules, Testing, Suite and the module template move to MIT, the core stays MPL-2.0

Part of the licence rule (decision issue filed alongside): barakoCMS core stays MPL-2.0, every module moves to MIT.

## Change

- Keep the root `LICENSE` (MPL-2.0) for the core.
- Replace the 7 module `LICENSE` files (Accounting, Analytics.Umami, Email.Resend, Email.Smtp, Files, Import, Pwa) with MIT, and add an MIT `LICENSE` to every module folder that has none.
- `PackageLicenseExpression` per package instead of one value in `Directory.Build.props`: `MPL-2.0` for `barakoCMS`, `MIT` for each module, `BarakoCMS.Testing`, `BarakoCMS.Suite` and the module template default (`TEMPLATE_LICENSE`).
- The licence line in each module `README.md`.
- A `changelog.d` fragment under Changed, and module version bumps so every module republishes under MIT.
- A check in `scripts/preflight.sh` or CI that each package's `PackageLicenseExpression` matches the rule, so a new module does not inherit MPL-2.0 by accident.

Historical CHANGELOG entries stay as written.

## Done when

- `dotnet pack` of a module produces a package whose licence is MIT, and the core's is MPL-2.0.
- NuGet shows MIT on the next published version of every module.

Plan page: https://claude.ai/code/artifact/09aef3dd-936d-432a-8056-9ef9bccfe8df

Start with the root LICENSE, the seven named module LICENSE files, Directory.Build.props, module README.md files, changelog.d, and scripts/preflight.sh to map the package metadata and licensing rule. Run dotnet pack for a module and the core, then verify the resulting package licenses match MIT for modules and MPL-2.0 for barakoCMS; confirm the module version bumps and NuGet metadata are covered.

Written by the indexing model from the issue text.