Support runtime environment changes via scope (sync to native Scope.setEnvironment) #6991

Context

sentry-java 8.63.0 added Scope.setEnvironment/getEnvironment (sentry-java#5772, proposal sentry-java#5769). It is applied to events, the DSC, logs, metrics and profiles. sentry-cocoa already has -[SentryScope setEnvironment:], and sentry-native has sentry_set_environment.

Problem

In RN, environment can only be set at init (options.environment). That value goes to native once, in RNSentryStart and on iOS. If an app changes environment at runtime, native-captured events (native crashes, ANRs, app-exit/NDK events, native logs and profiles) keep the init-time value.

Blocker

JS @sentry/core's Scope has no environment API, so there's nothing on the JS side to sync over the bridge.

Proposal

1. Upstream: ask sentry-javascript for a scope-level setEnvironment (or find out whether they plan one).
2. Once that exists: sync it to native through the scope-sync path on both platforms (Android Scope.setEnvironment, iOS SentryScope setEnvironment:), on both architectures. This adds a bridge spec method, so it needs a fallback for older native binaries.

Until then, this is parked.