feat(ui): add mobile-responsive layout with hamburger drawer

Adds MobileHeader with hamburger button (left-aligned) that opens a
slide-in sidebar drawer on mobile. Desktop layout is unchanged. All
hardcoded multi-column grids updated with responsive Tailwind breakpoints.

Co-Authored-By: Jack Levy

frontend/app/bills/[id]/page.tsx

@@ -78,8 +78,8 @@ export default function BillDetailPage({ params }: { params: Promise<{ id: strin
       </div>
 
       {/* Content grid */}
-      <div className="grid grid-cols-3 gap-6">
-        <div className="col-span-2 space-y-6">
+      <div className="grid grid-cols-1 md:grid-cols-3 gap-4 md:gap-6">
+        <div className="md:col-span-2 space-y-6">
           <AIBriefCard brief={bill.latest_brief} />
           <ActionTimeline actions={bill.actions} />
         </div>

frontend/app/members/page.tsx

@@ -56,7 +56,7 @@ export default function MembersPage() {
       ) : (
         <>
           <div className="text-sm text-muted-foreground">{data?.total ?? 0} members</div>
-          <div className="grid grid-cols-2 gap-3">
+          <div className="grid grid-cols-1 sm:grid-cols-2 gap-3">
             {data?.items?.map((member) => (
               <div key={member.bioguide_id} className="bg-card border border-border rounded-lg p-4 flex items-start justify-between gap-3">
                 <div className="flex-1 min-w-0">

frontend/app/page.tsx

@@ -40,8 +40,8 @@ export default function DashboardPage() {
       {isLoading ? (
         <div className="text-center py-20 text-muted-foreground">Loading dashboard...</div>
       ) : (
-        <div className="grid grid-cols-3 gap-8">
-          <div className="col-span-2 space-y-4">
+        <div className="grid grid-cols-1 md:grid-cols-3 gap-4 md:gap-8">
+          <div className="md:col-span-2 space-y-4">
             <h2 className="font-semibold flex items-center gap-2">
               <BookOpen className="w-4 h-4" />
               Your Feed

frontend/app/settings/page.tsx

@@ -119,7 +119,7 @@ export default function SettingsPage() {
         </h2>
         {stats ? (
           <>
-            <div className="grid grid-cols-3 gap-4">
+            <div className="grid grid-cols-1 sm:grid-cols-3 gap-4">
               <div className="bg-muted/50 rounded-lg p-3 text-center">
                 <FileText className="w-4 h-4 mx-auto mb-1 text-muted-foreground" />
                 <div className="text-xl font-bold">{stats.total_bills.toLocaleString()}</div>

frontend/app/topics/page.tsx

@@ -37,7 +37,7 @@ export default function TopicsPage() {
         </p>
       </div>
 
-      <div className="grid grid-cols-2 gap-3">
+      <div className="grid grid-cols-1 sm:grid-cols-2 gap-3">
         {TOPICS.map(({ tag, label, desc }) => (
           <div key={tag} className="bg-card border border-border rounded-lg p-4 flex items-start justify-between gap-3">
             <div>