feat(alerts): price alert configuration UI (#1057)

[chidii]

Closes #1057

Summary

Adds the creator key price alert configuration UI on top of the existing alert
backend. The notification trigger and auto-disable pipeline already exists in
processPriceAlerts (src/services/notification.service.ts) and is verified
by src/services/__tests__/priceAlerts.test.ts — this PR only adds the UI layer
that was missing.

Scope

• Set alert button on the key detail page
• Alert config modal: above/below direction, target price input
• Active alerts list in user settings with edit and delete
• In-app notification triggered when the alert condition is met
  (handled by the existing processPriceAlerts service)
• Alert auto-disabled after triggering once
  (handled by the existing PATCH /alerts/:alertId/triggered call)

Changes

• src/services/alert.service.ts — add createAlert, updateAlert, deleteAlert
  (POST /alerts, PATCH /alerts/:id, DELETE /alerts/:id)
• src/lib/queryKeys.ts — alerts.detail(userId, alertId)
• src/hooks/usePriceAlerts.ts — react-query hooks for list/create/update/delete;
  delete performs an optimistic cache update so the row disappears immediately
• src/components/common/PriceAlertModal.tsx — direction radio + target price input
  with validation that rejects a target on the wrong side of the current price
• src/components/common/PriceAlertButton.tsx — "Set price alert" button + modal
• src/components/common/ActivePriceAlertsList.tsx — list with edit and delete
• src/pages/CreatorDetailPage.tsx — renders <PriceAlertButton> next to the Buy button
• src/pages/ProfilePage.tsx — new "Price Alerts" tab that renders the list

Acceptance criteria

• Alert modal validates target price against current price direction
  — validateTargetPrice rejects an "above" target ≤ current and a "below"
  target ≥ current
• Active alerts listed correctly in user settings
  — ActivePriceAlertsList fetches from GET /alerts?userId=...&active=true
• Edit updates alert config correctly
  — useUpdatePriceAlert → PATCH /alerts/:id and refetches the list
• Delete removes alert from list immediately
  — optimistic removal in useDeletePriceAlert.onMutate
• In-app notification created correctly when price crosses threshold
  — existing processPriceAlerts covers this; see
  src/services/__tests__/priceAlerts.test.ts

Notes

• The trigger + auto-disable was already implemented server-side; this PR does
  not touch that path.
• No new dependencies.

[drips-wave]

@chidii Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits