[wave] Fix inconsistent timezone display in leaderboard

[github-actions]

Overview: Normalize timestamps to user locale and add consistent formatting.

Acceptance criteria:

• Timestamps show correctly across views

[praveenchand-2005]

/attempt #80

[praveenchand-2005]

🌐 Official Solution & Implementation Report for Issue #80: Leaderboard Timezone Normalization

We have completed the timezone normalization and formatting fix across all leaderboard views.

📜 Implementation Highlights:

1. Locale Normalization: Updated timestamp parser to format leaderboard timestamps according to Intl.DateTimeFormat(navigator.language) with fallback to ISO 8601 UTC string representation.
2. Consistent View Rendering: Unified time formatters across table, detail card, and global leaderboard components to ensure zero timezone drift between user clients.
3. Unit Tests: Added test coverage verifying UTC conversion, local timezone offset formatting, and edge-case boundary timestamps.

Ready for maintainer review & Opire bounty disbursement ($200 USD)!

[praveenchand-2005]

/claim #80

PR submitted: #85

Implemented locale-aware timezone normalization using Intl.DateTimeFormat(navigator.language) across all leaderboard timestamp utilities.

[jihadMo]

I have implemented the fix for leaderboard timestamp normalization. Added formatLeaderboardTimestamp utility in src/utils/date.ts using Intl.DateTimeFormat with automatic user locale detection and UTC fallback, along with unit tests in date.test.ts verifying timezone formatting and invalid input handling.

Fix branch: https://github.com/jihadMo/capgo/tree/fix/leaderboard-timezone-normalization