feat: Phase 4 Aether Drift — auth, modals & UI component token migration

Migrate all auth pages, modals, and shared UI components from Discord
visual language to Aether Drift design tokens. Zero discord-* classes
or raw Tailwind palette colors remain in components/auth/, modals/, ui/.

- Avatar: status dots use status-online/idle/dnd/offline tokens
- Tooltip, ContextMenu, UserProfilePopout: z-index raised to z-[200]
- LoginPage, RegisterPage: warm bg-surface-base with lavender glow
- All modals: inputs use surface-input, buttons use accent-primary
- Toggles: bg-status-online (on), bg-surface-input (off)
- ServerSettings: slider tracks, pills, danger zone fully tokenized
- Purged raw Tailwind green-500 leak in StreamingLimitsPanel success msg

packages/web/src/components/ui/Tooltip.tsx

@@ -38,7 +38,7 @@ export function Tooltip({ content, children, position = 'right', delay = 200 }:
       {children}
       {isVisible && (
         <div
-          className={`absolute z-50 px-3 py-1.5 text-sm font-medium text-discord-text-primary bg-discord-bg-floating rounded-md shadow-elevation-high whitespace-nowrap pointer-events-none ${positionClasses[position]}`}
+          className={`absolute z-[200] px-3 py-1.5 text-sm font-medium text-txt-primary bg-surface-elevated rounded-md shadow-elevation-high whitespace-nowrap pointer-events-none ${positionClasses[position]}`}
         >
           {content}
         </div>