Update exchange list & reformat country names.

[bigpoppa-sys]

What changed

• replaced the exchange list with Bitget, Gate, KuCoin, MEXC, HTX, and LBank
• added local logo assets for the newly listed exchanges
• shortened the country label for United Arab Emirates to UAE
• added a lightweight mock public-data mode so Overview / Network / Governance can render locally even when the anonymous backend is unavailable
• added a dev:mock script to start the frontend against the mock public data layer
• added a small formatter test covering the UAE country-name mapping

Why

The exchange panel and country naming needed a content refresh, and the public preview backend was intermittently unavailable during local review. Adding a mock public-data mode keeps the frontend reviewable even when the live anonymous API is down.

Impact

• the homepage exchange grid now shows the requested venues and order
• country labels are shorter and cleaner in the location list
• local frontend review is unblocked with npm run dev:mock even without a working public backend

Validation

• npm run build
• CI=true npm test -- --watchAll=false --runInBand src/lib/formatters.test.js