docs(httpserver): correct tier from 4 to 3

httpserver depends on launcher (Tier 2), placing it at Tier 3.
With launcher corrected from Tier 5 to Tier 2, httpserver's tier
drops accordingly.

doc.go

@@ -0,0 +1,19 @@
+// Package httpserver provides a lifecycle-managed HTTP server built on chi.
+//
+// It implements [launcher.Component] so it integrates directly with the launcher
+// lifecycle (OnInit → OnStart → OnStop). It also embeds [chi.Router], giving callers
+// the full chi routing API: Get, Post, Route, Mount, Use, etc.
+//
+// No middleware is installed by default. Compose your stack with [WithMiddleware]:
+//
+//	srv := httpserver.New(logger, cfg,
+//	    httpserver.WithMiddleware(
+//	        httpmw.Recover(),
+//	        httpmw.CORS([]string{"*"}),
+//	        httpmw.RequestID(uuid.NewString),
+//	        httpmw.RequestLogger(logger),
+//	    ),
+//	)
+//	srv.Get("/health", healthHandler)
+//	srv.Route("/api/v1", func(r chi.Router) { ... })
+package httpserver