UI/UX redesign: unified refined-glass design system

- Add shared UI primitives: Button, Field/Input/Select, PageHeader,
  Section, Callout, Tabs, Disclosure
- Replace gradient buttons with single blue-accent btn-primary
- Reserve gradient text for the brand wordmark only
- Rework Scanner page onto the glass system; collapse explainer and
  glossary into a disclosure, move filters into a glass toolbar
- Restructure Ticker Detail into tabs (Analysis / Indicators / S/R)
  with chart and recommendation always visible
- Align Watchlist, Rankings, Admin, Login/Register to shared primitives
- Unify stray indigo/violet/gray accents into the blue family

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/components/watchlist/AddTickerForm.tsx

@@ -24,7 +24,7 @@ export function AddTickerForm() {
       <button
         type="submit"
         disabled={addMutation.isPending || !symbol.trim()}
-        className="btn-gradient px-4 py-2 text-sm disabled:opacity-50 disabled:cursor-not-allowed"
+        className="btn-primary px-4 py-2 text-sm disabled:opacity-50 disabled:cursor-not-allowed"
       >
         <span>{addMutation.isPending ? 'Adding…' : 'Add'}</span>
       </button>