docs: travel time calibration New page covering what the feature measures, how to run it, and the covers that cannot be measured at all — Somfy RTS and kin report arrival the instant they are commanded, so they take a hand-entered time instead. Those are also the covers with most to gain, since they have no position reading for a card to draw, so the page leads with that rather than treating it as a footnote. Flags the two things a user should know before pressing the button: their covers will move end to end on their own for a few minutes, and nothing else can command them while it happens — including weather safety. Cancel and the `calibrating` control status are how that stays visible rather than looking like a fault. Cross-linked from the pages people will actually be on when they want it: the proxy cover (which animates automatically once a travel time exists, and is the route that works with any cover card), the Somfy RTS page, and Position Calibration — which has also moved under the new Calibration menu and now says so, since that is where people will go looking for it. What's New is untouched: it is keyed to released versions and this has not shipped yet.