[eli-r-ph]

💡 Motivation and Context

Stacked on #367.

Makes the v2 migration guide, changesets and godoc match what v2 does.
No behavior changes.

Changes

• Config: documents MaxBatchBytes, the optional MaxEventBytes, MaxRetryBackoff, and values Validate rejects.
• Request context: documents opt-in tracing headers and how context applies to identity calls.
• Group identify: documents that GroupIdentify.DistinctId is now sent.
• Errors: documents CaptureLocalError and the log line used without a Callback.
• Retries: documents which errors retry and how Retry-After is capped.
• Event IDs: documents UUIDv7 and how caller IDs are checked.
• Properties and AI events: fixes flag-property order and EnqueueAI details.
• Fixes stale changesets and godoc.
• Moves otel/package.json to 1.34.0 to match the latest otel tag.

💚 How did you test it?

• gofmt, go vet, go test -race and make api-diff pass; the API snapshot is unchanged.

🤖 Agent context

Autonomy: Human-driven (agent-assisted). Written with Claude Code; each claim was checked against the code.

🤖 Generated with Claude Code

[dustinbyrne]

The migration guide and changeset corrections match the implementation at this stack tip. Two optional wording clarifications below; neither prevents approval.

AI-assisted review.