[v6] Drop Module Federation v1 support and migrate fully to v2

## Motivation

Re.Pack currently ships two Module Federation implementations side by side: `ModuleFederationPluginV1` (built on webpack's/Rspack's native container API) and `ModuleFederationPluginV2` (built on `@module-federation/enhanced`). The generic `Repack.plugins.ModuleFederationPlugin` export still resolves to V1 and logs a notice on every build stating that the next major will repoint it at V2. v6 is that major.

MF v1 is no longer being iterated on upstream — all Module Federation development happens in the `@module-federation/*` v2 packages. Carrying both implementations doubles the plugin surface, the documentation, the tester apps and the test matrix, and it blocks a set of cleanups that only make sense once V1 is gone.

Part of #1414 (Roadmap to V6), which already lists MF v2+ as a minimum-version target and "updated docs for MF v2" as a deliverable.

## Breaking changes

- `Repack.plugins.ModuleFederationPlugin` starts resolving to the V2 implementation. Configs written against the V1 option shape need migrating.
- `ModuleFederationPluginV1` is removed.
- `@module-federation/enhanced` effectively becomes a required peer dependency instead of an optional one. V1 needed no extra install; V2 hard-fails without it (`ensureModuleFederationPackageInstalled` in `packages/repack/src/plugins/ModuleFederationPluginV2.ts`).
- The build-side `Federated` namespace (`createRemote`, `SHARED_REACT`, `SHARED_REACT_NATIVE` in `packages/repack/src/utils/federated.ts`) is removed — it is only consumed by V1.

## Scope

### Core

- [ ] Repoint `ModuleFederationPlugin` at the V2 implementation and drop the `beforeCompile` deprecation notice in `packages/repack/src/plugins/ModuleFederationPlugin.ts`
- [ ] Keep `ModuleFederationPluginV2` exported as an alias so existing v5 configs continue to work unchanged
- [ ] Remove `packages/repack/src/plugins/ModuleFederationPluginV1.ts`, its export from `plugins/index.ts`, and its unit tests
- [ ] Remove `packages/repack/src/utils/federated.ts` and its re-export from `utils/index.ts`
- [ ] Decide the fate of the client-side `Federated` namespace (`importModule`, `createURLResolver` in `packages/repack/src/modules/ScriptManager/federated.ts`) — superseded by the MF v2 resolver runtime plugin, but it is public API and may be used independently of the build plugin
- [ ] Move `@module-federation/enhanced` out of `peerDependenciesMeta.optional` and raise the peer floor to a 2.x range

### Apps and tests

- [ ] Migrate `apps/tester-federation` to V2, or fold it into `apps/tester-federation-v2` and delete it — once both are on V2 they largely duplicate each other, so consolidating into a single `tester-federation` app is probably the better outcome
- [ ] Drop the `with Module Federation v1` case in `tests/integration/src/plugins/NativeEntryPlugin.test.ts`
- [ ] Update the MF version matrix in the same file (currently 0.15.0 / 0.21.0 / 2.0.1) to match the new supported range

### Docs

- [ ] Remove `website/src/latest/api/plugins/module-federation-v1.mdx` and rename `module-federation-v2.mdx` to `module-federation.mdx`
- [ ] Rewrite `website/src/latest/docs/features/module-federation.md`, which currently just redirects readers to the Re.Pack 4.x docs with a caveat that they are out of date
- [ ] Add an MF v1 → v2 section to the v5 → v6 migration guide

## Prerequisite

This depends on first bumping `@module-federation/enhanced` in `packages/repack` from 0.8.9 to 2.x. That bump is a small standalone change but does have breakage of its own:

- `FederationRuntimePlugin` was renamed to `ModuleFederationRuntimePlugin` and `FederationHost` to `ModuleFederation`, affecting all three runtime plugins in `packages/repack/src/modules/FederationRuntimePlugins/`
- `runtimePlugins` widened to `(string | [string, Record])[]`, so `adaptRuntimePlugins` needs to handle the tuple form — which also unlocks passing options to runtime plugins
- the `jest.mock('@module-federation/enhanced/rspack')` automock in `ModuleFederationPluginV2.test.ts` no longer produces a constructor and needs an explicit factory

As a bonus, moving to `@module-federation/enhanced` >= 2.4.0 also releases the `webpack` hold at `~5.105.0` in `pnpm-workspace.yaml`, which exists solely because older MF versions depend on a webpack internal removed in 5.106.