chore(session): bump keyboard hint contrast + drop redundant font-sans

Two small ergonomic fixes after the impeccable pass:

- TaskLane keyboard hints (⏎ submit · ⇧⏎ newline) under each open input
  were rendered at text-muted-foreground/70, just shy of legible at a
  glance. Drop the /70 opacity modifier so they read at full muted weight
  on first look without becoming visually loud.

- 12 sites across the session screen had explicit font-sans utilities,
  but the body default is already IBM Plex Sans (via --font-sans in
  index.css and Tailwind v4's default-sans binding). None of the call
  sites sit inside a font-heading or font-mono cascade, so every
  font-sans there was a no-op. Drop them. ConcludeSessionModal also had
  three "text-xs font-sans text-xs" triplets — drop both the redundant
  font-sans and the doubled text-xs in one pass.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/components/assistant/ConcludeSessionModal.tsx

@@ -268,7 +268,7 @@ export function ConcludeSessionModal({
               )}
               <div
                 className={cn(
-                  'w-6 h-6 rounded-full flex items-center justify-center text-[0.6875rem] font-sans font-medium transition-colors',
+                  'w-6 h-6 rounded-full flex items-center justify-center text-[0.6875rem] font-medium transition-colors',
                   step === s
                     ? 'bg-primary text-white'
                     : (i < ['select-outcome', 'add-notes', 'summary'].indexOf(step))
@@ -280,7 +280,7 @@ export function ConcludeSessionModal({
               </div>
               <span
                 className={cn(
-                  'text-xs font-sans text-xs',
+                  'text-xs',
                   step === s ? 'text-foreground' : 'text-muted-foreground'
                 )}
               >
@@ -329,7 +329,7 @@ export function ConcludeSessionModal({
             <div className="space-y-4">
               {/* Selected outcome badge */}
               <div className="flex items-center gap-2">
-                <div className={cn('px-3 py-1.5 rounded-lg flex items-center gap-2 text-xs font-sans text-xs', selectedOutcome.bg, selectedOutcome.border, 'border')}>
+                <div className={cn('px-3 py-1.5 rounded-lg flex items-center gap-2 text-xs', selectedOutcome.bg, selectedOutcome.border, 'border')}>
                   <selectedOutcome.icon size={14} className={selectedOutcome.color} />
                   <span className={selectedOutcome.color}>{selectedOutcome.label}</span>
                 </div>
@@ -342,7 +342,7 @@ export function ConcludeSessionModal({
               </div>
 
               <div>
-                <label className="font-sans text-[0.625rem] uppercase tracking-widest text-muted-foreground block mb-2">
+                <label className="text-[0.625rem] uppercase tracking-widest text-muted-foreground block mb-2">
                   Additional Notes (optional)
                 </label>
                 <textarea
@@ -383,7 +383,7 @@ export function ConcludeSessionModal({
             <div className="space-y-4">
               {/* Outcome badge */}
               {selectedOutcome && (
-                <div className={cn('px-3 py-1.5 rounded-lg inline-flex items-center gap-2 text-xs font-sans text-xs', selectedOutcome.bg, selectedOutcome.border, 'border')}>
+                <div className={cn('px-3 py-1.5 rounded-lg inline-flex items-center gap-2 text-xs', selectedOutcome.bg, selectedOutcome.border, 'border')}>
                   <selectedOutcome.icon size={14} className={selectedOutcome.color} />
                   <span className={selectedOutcome.color}>{selectedOutcome.label}</span>
                 </div>
@@ -396,7 +396,7 @@ export function ConcludeSessionModal({
                   style={{ borderColor: 'var(--color-border-default)' }}
                 >
                   <div className="flex items-center justify-between mb-3">
-                    <span className="font-sans text-[0.625rem] uppercase tracking-widest text-muted-foreground flex items-center gap-1.5">
+                    <span className="text-[0.625rem] uppercase tracking-widest text-muted-foreground flex items-center gap-1.5">
                       <Sparkles size={10} className="text-primary" />
                       Ticket Notes
                     </span>
@@ -488,7 +488,7 @@ export function ConcludeSessionModal({
                   style={{ borderColor: 'var(--color-border-default)' }}
                 >
                   <div className="flex items-center justify-between mb-3">
-                    <span className="font-sans text-[0.625rem] uppercase tracking-widest text-muted-foreground flex items-center gap-1.5">
+                    <span className="text-[0.625rem] uppercase tracking-widest text-muted-foreground flex items-center gap-1.5">
                       <Sparkles size={10} className="text-primary" />
                       Status Update
                     </span>