board: the FAB and the undo snackbar rode behind the keyboard

Found by the Scaffold audit #2951 asked for. Three Scaffolds exist; the editor
and the sync screen both consume the IME inset, and the board consumed nothing.

`enableEdgeToEdge()` makes the manifest's `adjustResize` a no-op on API 30+, so
nothing resizes for the keyboard unless the app asks — and
`ScaffoldDefaults.contentWindowInsets` is systemBars, which the IME is not part
of. The Scaffold positions the FAB and the snackbar host from that value, so
with the search field focused both sat under the keyboard.

Not theoretical, and newly load-bearing: `3f0eef1` put an UNDO on the trash
snackbar, so the one control you could not reach was the one that takes back a
note you did not mean to throw away — reachable by searching, long-pressing a
hit and trashing it.

`union` rather than `add`: the navigation bar and the IME are the same edge,
not two stacked ones, and adding them would inset twice under a keyboard that
already covers the nav bar. Set once on the Scaffold rather than per-slot, so
the content column shrinks with it and the board's cards stay above the
keyboard instead of scrolling under it.

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

android/app/src/main/java/com/fabledsword/thoughtsync/ui/BoardScreen.kt

@@ -6,11 +6,14 @@ import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.PaddingValues
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.ime
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.union
 import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.staggeredgrid.LazyVerticalStaggeredGrid
 import androidx.compose.foundation.lazy.staggeredgrid.StaggeredGridCells
@@ -37,6 +40,7 @@ import androidx.compose.material3.ModalDrawerSheet
 import androidx.compose.material3.ModalNavigationDrawer
 import androidx.compose.material3.NavigationDrawerItem
 import androidx.compose.material3.Scaffold
+import androidx.compose.material3.ScaffoldDefaults
 import androidx.compose.material3.SnackbarDuration
 import androidx.compose.material3.SnackbarHost
 import androidx.compose.material3.SnackbarHostState
@@ -138,6 +142,21 @@ fun BoardScreen(
         },
     ) {
         Scaffold(
+            // The IME, added to what the Scaffold already insets for. `enableEdgeToEdge`
+            // makes the manifest's `adjustResize` a no-op on API 30+, so nothing resizes
+            // for the keyboard unless the app asks — and `ScaffoldDefaults.contentWindowInsets`
+            // is systemBars, which the IME is not part of. The Scaffold positions the FAB
+            // AND the snackbar host from this value, so without it both sit behind the
+            // keyboard whenever the search field has focus. That is not theoretical: the
+            // undo on a trashed search hit is exactly the control you cannot reach.
+            //
+            // `union` rather than `add` — the two are the same edge, not two stacked ones.
+            // Adding them would inset by the navigation bar a second time underneath a
+            // keyboard that already covers it.
+            //
+            // One owner for the edge, as with the search bar's missing statusBarsPadding:
+            // set here, the content Column gets it through `padding` and must not repeat it.
+            contentWindowInsets = ScaffoldDefaults.contentWindowInsets.union(WindowInsets.ime),
             snackbarHost = { SnackbarHost(snackbars) },
             floatingActionButton = {
                 // The + is the ONLY way in, by design: one obvious target rather