[Feature]: support first-party proxy CDN for Segment analytics

### Summary

Add support for loading Segment analytics through a first-party proxy CDN (`e.decentraland.org`) to bypass ad blockers. This mirrors the work done in `decentraland-dapps` ([#814](https://github.com/decentraland/decentraland-dapps/pull/814)) and `marketplace` ([#2679](https://github.com/decentraland/marketplace/pull/2679)).

### Problem / Motivation

Ad blockers drop all requests to `cdn.segment.com` and `api.segment.io`, causing sessions behind an ad blocker to send zero analytics events. Serving the analytics bundle and track API from a first-party domain (`e.decentraland.org`) avoids filter-list matches and recovers those sessions.

### Priority

High — blocks an important flow or initiative

### Target audience

All users

### Area

Tracking / Analytics

### Proposed Solution

1. Make the Segment analytics.js CDN URL configurable via `SEGMENT_ANALYTICS_URL` in `src/config/env/*.json` (dev only initially; stg/prd stay on default Segment CDN).
2. Make the Segment track API URL configurable via `SEGMENT_TRACK_URL` in `src/config/env/*.json` (dev only initially).
3. Update `DeferredAnalyticsProvider.tsx` to pass the proxy CDN URL to `@dcl/hooks` `AnalyticsProvider` (or configure `@segment/analytics-next` directly).
4. Update `segmentBeacon.ts` to read the track URL from config instead of the hardcoded `api.segment.io` constant.
5. Update `segmentConfig.ts` to expose the new config values.

### Acceptance Criteria

- [ ] `SEGMENT_ANALYTICS_URL` config key added to `dev.json`
- [ ] `SEGMENT_TRACK_URL` config key added to `dev.json`
- [ ] SDK path loads analytics.js from the proxy URL when configured
- [ ] Beacon transport uses the proxy track URL when configured
- [ ] Falls back to default Segment URLs when config is absent (stg/prd)
- [ ] Existing tests pass; new tests cover the proxy configuration
- [ ] Build passes