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/handlers/auth.go

@@ -117,11 +117,11 @@ func (hdlr *Handlers) executeLogin(
 		request, clientID, sessionID, nick,
 	)
 
-	hdlr.setAuthCookie(writer, request, token)
+	hdlr.setAuthCookie(writer, token)
 
 	hdlr.respondJSON(writer, request, map[string]any{
-		"id":   sessionID,
-		"nick": nick,
+		"id":    sessionID,
+		nickKey: nick,
 	}, http.StatusOK)
 }
 
@@ -177,6 +177,6 @@ func (hdlr *Handlers) handlePass(
 	}
 
 	hdlr.respondJSON(writer, request,
-		map[string]string{"status": "ok"},
+		map[string]string{statusKey: "ok"},
 		http.StatusOK)
 }