feat: add abort controller hook, toast tests, type exports, and date utils

[devwums]

Summary

This PR addresses four issues across reliability, testing, types, and internationalization:

• Request Cancellation: Added useAbortController hook in src/hooks/useAbortController.ts - returns a stable getSignal() function that aborts the previous in-flight request each time it is called and cleans up automatically on component unmount, preventing memory leaks and stale state updates
• Component Integration Tests: Added src/components/ui/tests/Toast.test.tsx with integration tests covering rendering by type (info/success/error), message display, and close button interaction
• Public Type Exports: Added src/types/index.ts as a barrel that re-exports all public types from �pi.ts and �nalytics.ts - consumers can now import from @/types instead of individual files
• Date/Time Localization: Added src/utils/dateUtils.ts with ormatDate, ormatShortDate, ormatTime, and ormatRelative - all built on Intl.DateTimeFormat and Intl.RelativeTimeFormat so they automatically respect the user's locale and timezone

Changes

• src/hooks/useAbortController.ts - abort controller hook with auto-cleanup on unmount
• src/components/ui/tests/Toast.test.tsx - Toast component integration tests
• src/types/index.ts - public type barrel export
• src/utils/dateUtils.ts - locale-aware date and time formatting utilities

closes #175
closes #176
closes #180
closes #181

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