City-level rankings and leaderboard breakdowns

[pradipNP]

Summary

Add city-level leaderboard views and city rank badges to extend the country ranking functionality introduced in #25.

Motivation

Country rankings are now available, but developers still cannot see how they rank within their own city. Local city rankings provide more meaningful and achievable goals for community engagement.

Proposed Features

• Add city extraction and normalization from developer location data
• Add city leaderboard filtering within a selected country
• Show city rank badges on developer profiles (e.g. Dev/sajee/dev card #1 in Berlin)
• Display city rank population counts
• Handle developers with missing or unrecognized city data gracefully
• Reuse the existing ranking infrastructure added for country rankings

Related

• Completes the remaining city-level scope from Country and city leaderboards #25
• Can be used as a foundation for future ranking enhancements

[pradipNP]

I'd like to work on this.