fix(mobile): plan landscape collapse + person picker, Odin page scroll, plan toolbar stacking

- PlanGrid maxHeight gets a 360px floor: calc(100dvh - 240px) left
  <160px in phone landscape and the rows vanished under the sticky
  header
- Phones get a person picker above the plan grid (one column at a
  time, defaults to the logged-in user) - the multi-person grid never
  fit a portrait viewport; desktop unchanged
- Odin chat height uses 100svh instead of 100dvh: dvh grows live as
  Android Chrome collapses its address bar, so the page always allowed
  a chrome-height scroll; svh sizes for the bar-visible viewport
  (verified zero overflow at 390x844 via Playwright)
- Plan toolbar stacks into full-width rows on xs (headerActionsSx
  pattern from the detail pages); Dnes/arrows and Tyden/Mesic stay
  paired on one row each

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/components/odin/OdinChat.tsx

@@ -422,7 +422,12 @@ export default function OdinChat() {
   return (
     <Box
       sx={{
-        height: "calc(100dvh - 100px)",
+        // svh (NOT dvh): dvh grows live as the mobile URL bar collapses, so a
+        // dvh-sized full-height layout always lets the page scroll by the
+        // browser-chrome height. svh sizes for the bar-visible viewport — the
+        // page never scrolls and the chat's message list scrolls internally.
+        // Desktop: svh === vh.
+        height: "calc(100svh - 100px)",
         display: "flex",
         border: 1,
         borderColor: "divider",