feat(symbol-page): aria-pressed PeriodTabs + sticky orderbook in 1D mode

PeriodTabs (reviewer 488fb32 concern):
- Drop role=tablist/tab/aria-selected. These imply a full ARIA tab
  pattern (tabpanel, aria-controls, roving tabIndex, internal Arrow
  focus traversal) which we don't implement — page-level left/right keys
  drive period change instead. Switch to plain button group with
  aria-pressed={active}, which accurately describes a segmented
  toggle. Comment updated to match.

OrderbookPanel sticky (new slice):
- Add optional sticky prop. When true, panel uses 'sticky top-4' with
  a slightly heavier bg-zinc-900/80 + backdrop-blur so it stays
  legible over the panels scrolling behind it.
- page.tsx passes sticky={isIntraday} — only 1D (10m bars) mode
  benefits, since orderbook timeliness drops on daily+ charts and the
  fixed slot would harm sidebar layout stability there.

web/app/[code]/page.tsx

@@ -253,7 +253,7 @@ export default function CodePage({ params }: { params: { code: string } }) {
             </div>
             <div className="space-y-4">
               <SymbolSidebar code={code} />
-              <OrderbookPanel code={code} />
+              <OrderbookPanel code={code} sticky={isIntraday} />
               <PriceTargets code={code} current={current} onChange={setTargets} />
               <AlertsPanel code={code} name={chart?.name} current={current} />
               <InvestmentNote code={code} />