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/pages/PlanWork.tsx

@@ -667,19 +667,29 @@ export default function PlanWork() {
         </Box>
       )}
 
+      {/* Mobile: stacked full-width rows (same pattern as headerActionsSx on
+          the detail pages); sm+ keeps the single wrapping toolbar row. The
+          paired controls (Dnes/arrows, Týden/Měsíc) stay together as one
+          full-width row each. */}
       <Box
         sx={{
           display: "flex",
-          flexWrap: "wrap",
-          alignItems: "center",
+          flexDirection: { xs: "column", sm: "row" },
+          flexWrap: { sm: "wrap" },
+          alignItems: { xs: "stretch", sm: "center" },
           gap: 1.5,
           mb: 2,
         }}
       >
         {/* Nav buttons grouped so they stay on one row when the toolbar
               wraps on mobile. */}
-        <Box sx={{ display: "inline-flex", gap: 1 }}>
-          <Button variant="outlined" color="inherit" onClick={goToToday}>
+        <Box sx={{ display: "flex", gap: 1 }}>
+          <Button
+            variant="outlined"
+            color="inherit"
+            onClick={goToToday}
+            sx={{ flex: { xs: 1, sm: "0 0 auto" } }}
+          >
             Dnes
           </Button>
           <Button
@@ -701,8 +711,8 @@ export default function PlanWork() {
         </Box>
         <Box
           sx={{
-            flex: 1,
-            minWidth: 220,
+            flex: { sm: 1 },
+            minWidth: { sm: 220 },
             display: "flex",
             justifyContent: "center",
           }}
@@ -727,7 +737,11 @@ export default function PlanWork() {
         <Box
           role="group"
           aria-label="Měřítko zobrazení"
-          sx={{ display: "inline-flex", gap: 1 }}
+          sx={{
+            display: "flex",
+            gap: 1,
+            "& > button": { flex: { xs: 1, sm: "0 0 auto" } },
+          }}
         >
           <Button
             variant={view === "week" ? "contained" : "outlined"}