fix(httpserver): guard OnStop against nil srv when OnStart was never called

If a component earlier in the launcher sequence fails during OnInit or OnStart,
the launcher calls OnStop on every already-registered component for cleanup.
httpserver.OnStop previously called s.srv.Shutdown(ctx) unconditionally; because
s.srv is only assigned inside OnStart, any shutdown triggered before OnStart ran
caused a nil pointer panic.

Add an early return in OnStop: `if s.srv == nil { return nil }`.

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to this module will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this module adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.9.1] - 2026-03-21
+
+### Fixed
+
+- `OnStop` now returns `nil` immediately when `s.srv == nil`, preventing a nil pointer
+  panic when the launcher calls cleanup on a server component whose `OnStart` was never
+  reached (e.g. because an earlier component failed during startup).
+
 ## [0.9.0] - 2026-03-18
 
 ### Added
@@ -25,4 +33,5 @@ and this module adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.
 - No middleware is installed by default; the full middleware stack is composed explicitly via `WithMiddleware` at construction time, keeping the stack visible and ordering unambiguous in the application source
 - chi was chosen as the underlying router because it uses stdlib `http.Handler` throughout, making it fully compatible with `httpmw` middleware and `httputil` handler adapters without any wrapper code at the boundary
 
+[0.9.1]: https://code.nochebuena.dev/go/httpserver/releases/tag/v0.9.1
 [0.9.0]: https://code.nochebuena.dev/go/httpserver/releases/tag/v0.9.0