feat: keep error status until polling recovers, classify unconfirmed deliveries, document the UI

- the poll loop now clears its error status after the next successful getUpdates, not before the retry, so a slow retry never shows as healthy
- recovery is reported only when getUpdates itself failed
- a send that may have reached Telegram is reported as unconfirmed instead of failed
- README and CHANGELOG describe the states, toasts, queue preview and spinner text

tests/status.test.ts

@@ -388,6 +388,7 @@ test("Error summaries turn transport failures into a short state and next step",
     ["Telegram API getUpdates failed: HTTP 502: Bad Gateway", "retrying", "Telegram unavailable", "retrying"],
     ["Unable to connect. Is the computer able to access the url?", "retrying", "offline", "retrying"],
     ["fetch failed", "retrying", "offline", "retrying"],
+    ["Telegram API sendRichMessage may have committed before transport failed.", "attention", "delivery unconfirmed", undefined],
     ["typing failed", undefined, undefined, undefined],
     ["settingsManager.reload is not a function", undefined, undefined, undefined],
   ];