Public tree view: full-width canvas like the member view

The public layout forced max-w-5xl on every /p page, so the tree chart was
cramped. Mirror the member shell: the public layout now drops the max-width for
the tree page (/p/<id>) only, giving the chart the full canvas (74vh to match
the member view), while the page keeps its heading and people list in a
centered max-w-5xl column. Person detail (/p/<id>/persons/<pid>) and /explore
stay narrow.

tsc clean; next build passes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

frontend/app/p/[treeId]/page.tsx

@@ -102,7 +102,7 @@ export default function PublicTreePage() {
 
   return (
     <div className="space-y-6">
-      <div>
+      <div className="mx-auto w-full max-w-5xl">
         <h1 className="font-serif text-3xl font-semibold">{tree?.name}</h1>
         {tree?.description && <p className="mt-1 text-[var(--muted)]">{tree.description}</p>}
         <p className="mt-1 text-sm text-[var(--muted)]">
@@ -110,6 +110,7 @@ export default function PublicTreePage() {
         </p>
       </div>
 
+      {/* Chart spans the full canvas (the layout removes max-width for /p/<id>). */}
       {focusId && people.length > 0 && (
         <PublicTreeChart
           people={people}
@@ -121,7 +122,7 @@ export default function PublicTreePage() {
         />
       )}
 
-      <div className="space-y-3">
+      <div className="mx-auto w-full max-w-5xl space-y-3">
         <h2 className="font-serif text-base font-semibold">All people</h2>
         <Input
           className="w-72"
@@ -131,7 +132,7 @@ export default function PublicTreePage() {
         />
       </div>
 
-      <Card className="overflow-hidden">
+      <Card className="mx-auto w-full max-w-5xl overflow-hidden">
         <CardContent className="p-0">
           {shown.length === 0 ? (
             <div className="px-4 py-6 text-sm text-[var(--muted)]">No matches.</div>