Re-vendor the canonical files from sneak/prompts at dd4027b (closes #112)

The shared files are fetched from sneak/prompts dd4027b, with this
repository's own entries after the shared content in .gitignore,
.editorconfig and .dockerignore.

Lint and tests are Dockerfile phases (golangci-lint v2.14.0, Debian Go
1.24.13) that the build stage depends on, and the Makefile targets call
the script/ entrypoints. make fmt also formats Markdown with prettier.

Fixes for the new lint findings: the auth cookie is always Secure, an
IRC connection's relay goroutine stops when the connection closes, and
repeated strings are constants.

Model: opus-5-5

internal/ircserver/server.go

@@ -81,22 +81,24 @@ func New(
 // start begins listening for TCP connections.
 //
 //nolint:contextcheck // long-lived server ctx, not the short Fx one
-func (s *Server) start(_ context.Context, addr string) error {
-	ln, err := net.Listen("tcp", addr)
+func (s *Server) start(ctx context.Context, addr string) error {
+	var listenConfig net.ListenConfig
+
+	ln, err := listenConfig.Listen(ctx, "tcp", addr)
 	if err != nil {
 		return fmt.Errorf("irc listen: %w", err)
 	}
 
 	s.listener = ln
 
-	ctx, cancel := context.WithCancel(context.Background())
+	serverCtx, cancel := context.WithCancel(context.Background())
 	s.cancel = cancel
 
 	s.log.Info(
 		"irc server listening", "addr", addr,
 	)
 
-	go s.acceptLoop(ctx)
+	go s.acceptLoop(serverCtx)
 
 	return nil
 }