fix: also send device user agent as $raw_user_agent

[lricoy]

💡 Motivation and Context

The SDK attaches the device user agent (http.agent) to every event as $user_agent, but PostHog's server-side classification — web analytics bot detection ($virt_is_bot and friends) and the materialized-column fast path — keys on the standardized $raw_user_agent property (the one posthog-js sends). posthog-android is the only mobile SDK putting a real device UA in $user_agent while omitting $raw_user_agent, so its events can't be classified without an expensive fallback.

PostHog/posthog#68253 removes that fallback for performance (it forced a full properties-blob read on every classification query — see the PR for production measurements), so this change mirrors the user agent into $raw_user_agent, aligning Android with the standardized property. Related: PostHog/posthog#68232.

$user_agent is still sent for backwards compatibility.

💚 How did you test it?

Agent-authored. Extended the existing PostHogAndroidContextTest dynamic-context test to assert $raw_user_agent carries the same value as $user_agent; relying on CI to run the suite (no local Android toolchain in this session).

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Ran pnpm changeset to generate a changeset file (changeset file added manually with the same format)

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Built with Claude Code as part of a cross-repo effort to standardize on $raw_user_agent (PostHog/posthog#68232, PostHog/posthog#68253, with sibling PRs to posthog-python and posthog-ruby). The value duplicated is the existing http.agent string; no truncation added since the current $user_agent isn't truncated either.

[greptile-apps]

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