Use one name for each thing the UI shows (closes #399)

The database target type is called an archive on its badge, in the add target form's type list and on its edit page, and its settings read "Archive expiry" and "Archive rotation" everywhere, the new webhook page included. The retry field is labelled "Delivery attempts", with its help text and error messages to match, on both target forms and in the target list, where a stored 0 shows as one attempt. The target list's other labels take the same capitalisation. The navbar says "Sign out" and the sign-in page "Sign in", and the README follows. The resubmit notice says "webhook". The stored values (`database`, `max_retries`) and their meaning are unchanged.

Model: opus-5-5

internal/handlers/auth.go

@@ -268,7 +268,7 @@ func (h *Handlers) rejectLogin(
 	)))
 	h.renderLoginError(
 		w, r,
-		"Too many failed login attempts. Please try again later.",
+		"Too many failed sign-in attempts. Please try again later.",
 		http.StatusTooManyRequests,
 	)
 }