fix: design system v4 polish — home icon, mobile hamburger, contrast, font-label cleanup

- Home sidebar icon: always cyan, bg-accent-dim only when route is "/"
- Mobile TopBar: add left padding so hamburger isn't hidden behind logo
- Landing page: bump card border color (#1e2130 → #2a2f3d) for better contrast
- Replace all font-label references (40 occurrences, 19 files) with font-mono or font-sans
- Remove deprecated --font-label CSS variable from index.css
- Convert hardcoded hex in layout inline styles to CSS variables (light-mode ready)
- Add @types/react-syntax-highlighter for script builder types

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/maintenance/BatchLaunchModal.tsx

@@ -96,7 +96,7 @@ export function BatchLaunchModal({ treeId, treeName, onClose, onLaunched }: Batc
               key={tab.id}
               onClick={() => setActiveTab(tab.id)}
               className={cn(
-                "flex items-center gap-1.5 px-3 py-2 font-label text-[0.6875rem] uppercase tracking-wide transition-colors",
+                "flex items-center gap-1.5 px-3 py-2 font-sans text-[0.6875rem] uppercase tracking-wide transition-colors",
                 activeTab === tab.id
                   ? "border-b-2 border-primary text-foreground"
                   : "text-muted-foreground hover:text-foreground"
@@ -112,7 +112,7 @@ export function BatchLaunchModal({ treeId, treeName, onClose, onLaunched }: Batc
         <div className="p-6">
           {activeTab === 'manual' && (
             <div className="space-y-2">
-              <label className="font-label text-[0.6875rem] uppercase tracking-wide text-muted-foreground">
+              <label className="font-sans text-[0.6875rem] uppercase tracking-wide text-muted-foreground">
                 Server names (one per line)
               </label>
               <textarea

frontend/src/components/maintenance/BatchStatusCard.tsx

@@ -86,7 +86,7 @@ export function BatchStatusCard({ session, targetLabel, treeId, batchId }: Batch
           <div className="flex items-center gap-2 mt-0.5">
             {isComplete && session?.outcome && (
               <span className={cn(
-                "font-label text-[0.625rem] uppercase tracking-wide rounded-full px-2 py-0.5",
+                "font-sans text-[0.625rem] uppercase tracking-wide rounded-full px-2 py-0.5",
                 OUTCOME_COLORS[session.outcome] ?? OUTCOME_COLORS.unresolved
               )}>
                 {OUTCOME_LABELS[session.outcome] ?? session.outcome}