Style group session dialog with the group's accent color

- Replace generic card/gray styling with the group's own tint, derived
  via color-mix so the dialog reads as a "window" version of the card
- Add 3px colored border, tinted header/footer panels, and softened
  border rules on todo rows to tie the whole dialog to one hue
- Give the Save button a solid accent background with theme-appropriate
  text color (white on light, dark on neon) for clear affordance

components/board/group-session-dialog.tsx

@@ -102,6 +102,14 @@ export function GroupSessionDialog({
   const color = useGroupColor(group.color);
   const accentColor = isDark ? color.dark : color.light;
   const todoTextColor = getBrighterColor(accentColor, isDark ? "dark" : "light");
+  // The group's card treatment, scaled to a window: the same hand-picked
+  // tint fill the card uses (blended into the theme's card surface), plus a
+  // softer version of the group's stroke for the header/footer rules so
+  // they read as the same hue without competing with the 3px border.
+  const dialogBackground = `color-mix(in srgb, ${isDark ? color.softDark : color.soft} 85%, var(--card))`;
+  const panelBackground = `color-mix(in srgb, ${isDark ? color.softDark : color.soft} 100%, var(--card))`;
+  const ruleColor = `color-mix(in srgb, ${accentColor} 40%, transparent)`;
+  const subtleRuleColor = `color-mix(in srgb, ${accentColor} 25%, transparent)`;
 
   const [noteDraft, setNoteDraft] = useState(group.noteContent);
   const [todoDrafts, setTodoDrafts] = useState<TodoDraft[]>(() => toDrafts(group.todos));
@@ -215,10 +223,16 @@ export function GroupSessionDialog({
         <DialogContent
           data-color-mode={colorMode}
           showCloseButton={false}
-          className="fixed top-[2vh] left-1/2 h-[96vh] max-h-[96vh] w-[calc(100%-1rem)] max-w-[calc(100%-1rem)] sm:max-w-5xl -translate-x-1/2 translate-y-0 flex flex-col gap-0 overflow-hidden p-0"
+          className="fixed top-[2vh] left-1/2 h-[96vh] max-h-[96vh] w-[calc(100%-1rem)] max-w-[calc(100%-1rem)] sm:max-w-5xl -translate-x-1/2 translate-y-0 flex flex-col gap-0 overflow-hidden rounded-2xl border-[3px] p-0 ring-0"
+          style={{ borderColor: accentColor, backgroundColor: dialogBackground }}
         >
-          <div className="flex shrink-0 items-center justify-between gap-2 border-b p-4">
+          <div
-            <DialogTitle className="min-w-0 truncate">{group.title}</DialogTitle>
+            className="flex shrink-0 items-center justify-between gap-2 border-b p-4"
+            style={{ borderColor: ruleColor, backgroundColor: panelBackground }}
+          >
+            <DialogTitle className="min-w-0 truncate" style={{ color: todoTextColor }}>
+              {group.title}
+            </DialogTitle>
             <div className="flex items-center gap-2">
               <span className="text-xs text-muted-foreground">
                 {savingAll || noteAutosave.isSaving ? "Saving…" : "Saved"}
@@ -273,7 +287,10 @@ export function GroupSessionDialog({
               </div>
 
               {completedTodoDrafts.length > 0 && (
-                <div className="space-y-2 rounded-md border">
+                <div
+                  className="space-y-2 rounded-md border"
+                  style={{ borderColor: ruleColor }}
+                >
                   <button
                     type="button"
                     onClick={() => setCompletedOpen((v) => !v)}
@@ -328,7 +345,10 @@ export function GroupSessionDialog({
             </div>
           </div>
 
-          <div className="flex shrink-0 flex-wrap items-center justify-between gap-2 border-t bg-muted/50 p-4">
+          <div
+            className="flex shrink-0 flex-wrap items-center justify-between gap-2 border-t p-4"
+            style={{ borderColor: ruleColor, backgroundColor: panelBackground }}
+          >
             <div className="flex flex-wrap items-center gap-2">
               <Button variant="outline" className="gap-2" onClick={addEmptyTodoDraft}>
                 <Plus className="size-4" />
@@ -343,7 +363,19 @@ export function GroupSessionDialog({
                 Ask AI
               </Button>
             </div>
-            <Button onClick={handleSaveAll} disabled={savingAll}>
+            <Button
+              onClick={handleSaveAll}
+              disabled={savingAll}
+              className="hover:brightness-110"
+              style={{
+                backgroundColor: accentColor,
+                borderColor: accentColor,
+                // The stroke is a darker ink on light themes (white type
+                // clears it) and a brighter neon on dark themes (dark type
+                // clears it) -- the same pairing the to-do text uses.
+                color: isDark ? "#18181b" : "#ffffff",
+              }}
+            >
               {savingAll ? "Saving…" : "Save"}
             </Button>
           </div>
@@ -482,7 +514,13 @@ function SessionTodoRow({
   );
 
   return (
-    <div className="space-y-2 rounded-md border p-3">
+    <div
+      className="space-y-2 rounded-md border p-3"
+      // A whisper of this group's own stroke on the row frame (see
+      // subtleRuleColor in GroupSessionDialog) so the rows tie into the
+      // card's color instead of generic gray rules.
+      style={{ borderColor: `color-mix(in srgb, ${accentColor} 25%, transparent)` }}
+    >
       <div className="flex items-start gap-2">
         {draft.isNew ? (
           <Tooltip>
@@ -545,7 +583,10 @@ function SessionTodoRow({
           preview="edit"
         />
       ) : draft.details ? (
-        <div className="max-h-40 overflow-y-auto rounded-md border p-2">
+        <div
+          className="max-h-40 overflow-y-auto rounded-md border p-2"
+          style={{ borderColor: `color-mix(in srgb, ${accentColor} 25%, transparent)` }}
+        >
           <MarkdownPreview source={draft.details} />
         </div>
       ) : null}