Phase 5: alert subscriptions UI + multiple watchlists + queue fixes

UI:
- /alerts page: event history with acknowledge, subscription create/manage with toggle
- /admin/smtp: SMTP config form (host, port, auth, test)
- Watchlist sidebar: dropdown selector for multiple watchlists, create/delete
- Sidebar: alerts count badge, SMTP link under admin
- Mobile tab nav: alerts tab added
- Client trpc.ts: all new API methods + types

Backend:
- watchlists.listByWatchlist procedure + listSymbolsByWatchlist repo fn
- yfinance min-interval 1500->2000ms to reduce Edge 429s
- Fixed e.date.slice error in yfinance-adjustments with typeof guard
- Removed defunct BITF from watchlist+queue
- Cleared 83 failed + 12 backoff queue jobs

Docs:
- FUNCTIONAL_DESIGN.md: alerts + multiple watchlists + SMTP documented
- TECH_DESIGN.md: new modules, tRPC procs, routes updated

app/src/components/MobileTabNav.tsx

@@ -18,6 +18,7 @@ const TABS: TabItem[] = [
   { label: "Overview", href: "/", icon: "📊" },
   { label: "Filings", href: "/filings", icon: "📄" },
   { label: "Options", href: "/options-dd", icon: "🔮" },
+  { label: "Alerts", href: "/alerts", icon: "🔔" },
   { label: "Execution", href: "/execution", icon: "⚡" },
   { label: "Trade Plan", href: "/trade-plan", icon: "📋" },
   { label: "Settings", href: "/settings", icon: "⚙️" },