feat(build): bake plugin metadata and the framework version into plugins.gen.go

- party.Info, party.Installed, party.Describe (additive; Plugin and Activate unchanged)
- summer build resolves plugin dirs with one go list, reads plugin.yaml, versions per D-07 (module version, git describe without --dirty, none for in-app plugins)
- build.EffectiveFramework: newest tag of a locally replaced or used framework checkout, else the go.mod require
- generated main calls party.Describe(app, PluginInfo, FrameworkVersion) before Activate; metadata failures warn and fall back to IDs
- summer new goldens and examples/hello regenerated

docs/plugins/marketplace.md

@@ -88,6 +88,10 @@ func TestPluginManifest(t *testing.T) {
 
 `kiosk.CheckT` runs the same check as `summer plugin:manifest --check` and names the command to rerun. A nested plugin gets its own test in its own directory.
 
+## Installed plugin metadata
+
+`summer build` reads the `plugin.yaml` of every plugin the application lists and bakes the name and description into the generated `plugins.gen.go` as `PluginInfo`, next to each plugin's version and the framework version (`FrameworkVersion`). At start-up the application publishes them as `party.Installed`, which the admin's Plugins screen reads. [Go modules and workspaces](../architecture/go-modules-and-workspaces.md#the-summeryaml-manifest) explains where the versions come from.
+
 ## Registry API v1
 
 summercms.io publishes the plugins it lists through a read-only JSON API. The marketplace pages, `summer` and the admin's Plugins screen read it. Its base path is `/api/registry/v1` (`kiosk.RegistryAPIPath`), and the `kiosk` module holds its wire types, so every client and the server share one definition of the shape.