fix: use deterministic locale in History date formatting

[EmeditWeb]

Problem

In History.tsx (line 10), toLocaleString() is called without a locale parameter. This produces different date formats depending on the user's browser locale, which can cause inconsistent display across users.

User impact: Users in different locales see different date formats, making the UI inconsistent.

Root Cause

The locale parameter was omitted during initial development.

What To Build

1. Add explicit 'en-US' locale parameter to toLocaleString() calls
2. Or create a formatDate utility in src/lib/formatDate.ts for consistent date formatting across the app

Files To Touch

• src/pages/History.tsx — line 10 add explicit locale
• src/lib/formatDate.ts — new utility (optional)

Acceptance Criteria

• Date format consistent across all browsers/locales
• No regression in date display

Mandatory Checks

• context/ files read
• npm run build passes
• PR references this issue