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_test.go

@@ -71,7 +71,9 @@ func newTestEnv(t *testing.T) *testEnv {
 		MOTD:       "Welcome to test IRC",
 	}
 
-	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	var listenConfig net.ListenConfig
+
+	listener, err := listenConfig.Listen(t.Context(), "tcp", "127.0.0.1:0")
 	if err != nil {
 		t.Fatalf("listen: %v", err)
 	}
@@ -116,10 +118,12 @@ func newTestEnv(t *testing.T) *testEnv {
 func (env *testEnv) dial(t *testing.T) *testClient {
 	t.Helper()
 
-	conn, err := net.DialTimeout(
+	dialer := net.Dialer{Timeout: testTimeout}
+
+	conn, err := dialer.DialContext(
+		t.Context(),
 		"tcp",
 		env.srv.Listener().Addr().String(),
-		testTimeout,
 	)
 	if err != nil {
 		t.Fatalf("dial: %v", err)
@@ -323,6 +327,7 @@ func TestPrivmsgBetweenClients(t *testing.T) {
 	bob.joinAndDrain("#chat")
 
 	alice.send("PRIVMSG #chat :hello bob!")
+
 	lines := bob.sendAndExpect("PING :sync", "hello bob!")
 	assertContains(t, lines, "hello bob!", "channel PRIVMSG")
 }