Turbo Modules: Documentation, migration guide, and public API

[alwx]

Land the user-facing story once the implementation stabilizes.

Tasks

• Public API: confirm the option name (enableTurboModuleTracking), the integration name (turboModulesIntegration), and the options bag (slowCallThresholdMs, ignoreTurboModules, top-N cap). Run through yarn api-report and lock the surface.
• CHANGELOG.md under Unreleased / Features.
• Coordinate a docs PR with the Sentry docs repo covering:
  • How the feature is enabled (new arch vs. old arch).
  • What data lands on spans (attributes, measurements) and on events (tags, contexts).
  • How crash reports attribute the active module + method.
  • Privacy / overhead notes — especially that method names are sent (so users on strict PII setups know what they're shipping).
• Add a section to packages/core/AGENTS.md describing the TurboModule perf logger plumbing so future contributors know where to look.
• Decide and document the deprecation story (if any) for the legacy NativeModules path — most users will migrate to the new arch over the next few RN versions, and the legacy path can be marked as best-effort.

[linear-code]

RN-644