docs(release): add 2.12.0 notes (#31)

Covers adopting modern-di 2.25's blessed integration seams
(add_providers, resolve_dependency) and the resulting floor bump.

Author: lesnik512

planning/releases/2.12.0.md

@@ -0,0 +1,39 @@
+# modern-di-litestar 2.12.0 — adopt modern-di 2.25 integration seams
+
+Maintenance release. **No public API change** — `ModernDIPlugin`, `FromDI`,
+`build_di_container`, and the context providers keep their signatures and
+behavior. It raises the `modern-di` floor and single-sources onto the new
+blessed integration seams from modern-di 2.25
+([modern-python/modern-di#283](https://github.com/modern-python/modern-di/pull/283)).
+
+## Internal refactors
+
+- **`container.add_providers()` replaces the `providers_registry` reach-in.**
+  `ModernDIPlugin.on_app_init` registers `_CONNECTION_PROVIDERS` through the
+  new blessed `Container.add_providers()` instead of reaching two attributes
+  deep into `container.providers_registry.add_providers()`. Same semantics,
+  less surface touched.
+- **`container.resolve_dependency()` replaces the `isinstance` dispatch.**
+  `_Dependency.__call__` no longer branches on
+  `isinstance(self.dependency, providers.AbstractProvider)` to choose between
+  `resolve_provider` and `resolve` — it calls the new
+  `Container.resolve_dependency()`, which does the same dispatch in core. As a
+  side effect its return type tightens from `T_co | None` to `T_co`: the
+  `None` case was never reachable (both underlying resolve paths raise rather
+  than return `None` on failure), so this fixes a type-only false negative,
+  not a runtime one.
+
+## Packaging
+
+- **`modern-di` floor raised to `>=2.25.0,<3`** (was `>=2.21.0`). The refactor
+  relies on `Container.add_providers()` and `Container.resolve_dependency()`,
+  added in `modern-di` 2.25.0.
+
+## Upgrade
+
+Bump `modern-di-litestar` to `2.12.0`; `pip`/`uv` will pull `modern-di>=2.25.0`.
+No code changes required.
+
+## Internals
+
+- 100% line coverage across Python 3.10–3.14; `ruff` and `ty` clean.