Add trackRevenue bridge for the native revenue API

[ahsanalidotme]

Closes linktrail-io/linktrail-backend#111

Blocked on release (native compile)

The iOS/Android bridge calls LinkTrail.trackRevenue / trackRevenueAsync, which exist only in unreleased native SDK PRs. The wrapper compiles against the published pins (LinkTrailSDK ~> 0.0.11, io.linktrail:sdk:0.0.5), so native builds will fail until the native SDKs are released and the pins in LinktrailReactNative.podspec / android/build.gradle are bumped (not done here: no version numbers invented). Do not merge/release before then.

• iOS SDK: https://github.com/linktrail-io/linktrail-ios-sdk-source/pull/22
• Android SDK: https://github.com/linktrail-io/linktrail-android-sdk-source/pull/13

Deploy order: backend -> native SDK releases -> wrappers (this PR, plus pin bump).

What

• LinkTrail.trackRevenue({ transactionId, value, currency, productId? }) -> Promise<{ id?, attributed, duplicate }>.
• TS-side validation/normalisation matching native rules (id trimmed, 1-255 chars; value finite >= 0; currency 3 letters, uppercased; blank productId dropped). Invalid input rejects with typed LinkTrailRevenueError (invalid_transaction_id / invalid_value / invalid_currency) without calling native.
• TurboModule spec + iOS (Swift/ObjC++) and Android (Kotlin) bridge via the async throwing native variants; native revenue errors map to the same codes.
• README section (react-native-iap / expo-iap / RevenueCat mapping; transactionId = StoreKit transaction id / Play orderId; dedupe makes retries safe), CHANGELOG Unreleased.
• First jest unit tests (native module mocked); adds jest devDependencies and npm test. CI workflow untouched (no .github/workflows changes), so CI does not run npm test yet.

Verified

• tsc clean, npm run lint 0 errors (3 pre-existing warnings), jest 16/16 passing.

Unverified

• iOS and Android native compile of the bridge code (needs the unreleased SDKs; not tried against local branch checkouts).
• Purchase-library snippets in the README are illustrative (field names of react-native-iap/expo-iap/RevenueCat not checked against their current typings).

Backend PR (deploy first): https://github.com/linktrail-io/linktrail-backend/pull/138
Dashboard PR: https://github.com/linktrail-io/linktrail-client-dashboard/pull/103

🤖 Generated with Claude Code