feat: add tenant and user management with migrations, handlers, and tests

- Implemented tenant and user management features including:
  - Tenant creation and management with associated migrations.
  - User creation and management with associated migrations.
  - Tenant membership management with associated migrations.
  - Platform user roles management with associated migrations.
  - Quota management with associated migrations.
  - Article and template management with associated migrations.
- Added HTTP handlers for templates and workspaces.
- Created tests for protected and public routes.
- Introduced a script to check tenant scope in SQL queries.
- Documented task plan for backend completion and frontend foundation.

server/internal/shared/auth/context.go

@@ -0,0 +1,28 @@
+package auth
+
+import "context"
+
+type Actor struct {
+	UserID   int64
+	TenantID int64
+	Role     string
+}
+
+type actorKey struct{}
+
+func WithActor(ctx context.Context, actor Actor) context.Context {
+	return context.WithValue(ctx, actorKey{}, actor)
+}
+
+func ActorFromCtx(ctx context.Context) (Actor, bool) {
+	actor, ok := ctx.Value(actorKey{}).(Actor)
+	return actor, ok
+}
+
+func MustActor(ctx context.Context) Actor {
+	actor, ok := ActorFromCtx(ctx)
+	if !ok {
+		panic("auth: actor not in context")
+	}
+	return actor
+}