Show the whole IP lookup answer, @meta included, on the home page (closes #201)

The home page's IP lookup card showed only the answer's `data` part, or
only the message of an error answer. It now shows the whole answer,
`@meta` included, as the IP information API card does.

The server already added `@meta` to every JSON answer. A new table test
requests every JSON route and checks `@meta` and its fields. It covers
successes, the errors the handlers write, the router's 404 and 405, and
the 500 and 504 the middleware writes.

Model: opus-5-5

internal/server/handlers_internal_test.go

@@ -77,6 +77,7 @@ const (
 	prefixLengthPagePath = "/prefixlength/24"
 	statusJSONPath       = "/status.json"
 	statsPath            = "/api/v1/stats"
+	healthCheckPath      = "/.well-known/healthcheck.json"
 )
 
 // The names the stats handler tests report the two stats handlers by.
@@ -1109,7 +1110,7 @@ func TestJSONRoutesDoNotSendErrorDetails(t *testing.T) {
 		path     string
 		wantCode int
 	}{
-		{"/.well-known/healthcheck.json", http.StatusServiceUnavailable},
+		{healthCheckPath, http.StatusServiceUnavailable},
 		{statusJSONPath, http.StatusInternalServerError},
 		{statsPath, http.StatusInternalServerError},
 		{asJSONPath, http.StatusInternalServerError},