feat: add Load/Unload lifecycle hooks to PluginRegistration

Enables runtime plugin disable/enable without CMS restart.
Load is called after registration succeeds; Unload on disable
with a 30-second context deadline.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

plugin/registration.go

@@ -1,6 +1,7 @@
 package plugin
 
 import (
+	"context"
 	"io/fs"
 	"net/http"
 
@@ -38,6 +39,9 @@ type PluginRegistration struct {
 	DirectoryExtensions func() *DirectoryExtensions
 	MediaHooks          MediaHooksProvider
 
+	Load   func(deps ServiceDeps) error
+	Unload func(ctx context.Context) error
+
 	Dependencies []Dependency
 	Migrations   func() fs.FS
 	Version      string