feat(session): impeccable session-screen pass + tasklane keyboard flow

Multi-step UX refactor of the assistant chat session screen, run via the
$impeccable skill. Heuristic score moved 24/40 → 33/40 (+9), with the biggest
gains on Aesthetic & Minimalist (1→3), Consistency & Standards (1→3), and
Recognition Rather Than Recall (2→4).

Distill — chat region:
- Remove the "Suggested checks" chip strip + selected-chip detail card; the
  TaskLane is the single canonical home for "what to do next"
- Add an inline Next steps · N pending cue above the latest action-bearing
  AI bubble (anchors attention without duplicating the lane's items)
- Link banner ↔ script-panel lifecycle: collapsing or dismissing the
  ProposalBanner now also hides the InlineNoTemplateDialog / TemplateMatchPanel
- Drop backdrop-blur on the handoff-context overlay (DESIGN-SYSTEM hard rule)

Quieter — drop decoration overshoot:
- Remove 3px side stripes on TaskLane done cards, all 6 ProposalBanner modes,
  WhatWeKnowItem fact rows
- Drop bg-gradient surfaces on WhatWeKnow + every ProposalBanner mode
- Drop 2px accent borderTop on the TaskLane header
- Replace bordered avatar boxes in banners with inline state-colored icons
- Each surface now uses a single decoration channel (top border + inline icon)

Layout:
- Header consolidates to Resolve + Escalate + ⋯ kebab; Context, New Ticket,
  Update Ticket, Pause now live behind the kebab on desktop, with feature
  parity in the existing mobile overflow menu
- Messages column anchors to max-w-3xl mx-auto to match the composer
- Chat bubbles drop from rounded-2xl to rounded-xl for vocabulary alignment

Typeset:
- Unify text sizing from 14 distinct sizes (with sub-pixel oddities and
  rem/px duplicates) to a 5-step scale: 10px / 11px / text-xs / 13px / text-sm

WhatWeKnow collapsible:
- Header is now a toggle; section body hides when collapsed
- Auto-collapses on first render when facts ≥ 5 so Questions / Diagnostic
  Checks stay above the fold
- Engineer's choice persists in sessionStorage per session and beats the
  auto-collapse heuristic on subsequent renders
- key=activeChatId on both render sites resets state cleanly across sessions

Polish:
- Split MessageCircleQuestion into Pencil (question Answer CTA, write
  affordance) + HelpCircle (per-check Explain toggle, universal help icon) —
  same icon for two different jobs was a discoverability bug
- Drop redundant text-xs from font-sans text-[0.625rem] / text-[0.6875rem]
  double-class definitions; the more-specific size always wins

TaskLane keyboard flow:
- Enter submits and auto-advances to the next pending task; Shift+Enter
  inserts a newline (consistent across question and action textareas — paste
  events don't fire keydown, so paste-then-Enter still works as expected)
- Esc cancels (same as the Cancel button)
- After the last pending task is submitted, focus moves to the Send Responses
  button so the engineer can fire the whole batch with one more keystroke
- Subtle hint row under each open input teaches the shortcut

Type-check, lint, and build all clean.

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 text-xs font-medium transition-colors',
+                  'w-6 h-6 rounded-full flex items-center justify-center text-[0.6875rem] font-sans font-medium transition-colors',
                   step === s
                     ? 'bg-primary text-white'
                     : (i < ['select-outcome', 'add-notes', 'summary'].indexOf(step))
@@ -342,7 +342,7 @@ export function ConcludeSessionModal({
               </div>
 
               <div>
-                <label className="font-sans text-xs text-[0.625rem] uppercase tracking-widest text-muted-foreground block mb-2">
+                <label className="font-sans text-[0.625rem] uppercase tracking-widest text-muted-foreground block mb-2">
                   Additional Notes (optional)
                 </label>
                 <textarea
@@ -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-xs text-[0.625rem] uppercase tracking-widest text-muted-foreground flex items-center gap-1.5">
+                    <span className="font-sans 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-xs text-[0.625rem] uppercase tracking-widest text-muted-foreground flex items-center gap-1.5">
+                    <span className="font-sans text-[0.625rem] uppercase tracking-widest text-muted-foreground flex items-center gap-1.5">
                       <Sparkles size={10} className="text-primary" />
                       Status Update
                     </span>