fix(ios): forward all background URL session events to the SDK per docs

[jaymaycry]

Why

The background URL session handling added in 0.2.0 (#2) used an identifier-prefix check (handlesBackgroundURLSession) to route only MotionTag-owned sessions to the SDK. That is not what the MotionTag iOS guide prescribes, and not what MotionTag's official Flutter SDK AppDelegate does:

override func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
    MotionTagCore.sharedInstance.processBackgroundSessionEvents(with: identifier, completionHandler: completionHandler)
}

Every identifier is forwarded unconditionally — the SDK decides internally which sessions are its own. Verified against the SDK 6.5.0 binary: registerCallback:forIdentifier: stores the handler and only invokes it when the SDK's own session finishes events, so foreign handlers go stale rather than being double-called.

The prefix check was also fragile: a future SDK version changing its session identifier would silently break background-upload recovery again.

What

• plugin/withIosAppDelegate.js: generated override is now a plain unconditional forward (matches the Flutter reference; existing misplaced/old blocks are replaced on expo prebuild)
• ios/MotionTagBootstrap.swift: removed handlesBackgroundURLSession(identifier:)
• README.md: bare-RN snippet reverted to the docs pattern; identifier-prefix maintenance note dropped from the SDK-bump checklist

Note for consumers

handlesBackgroundURLSession existed only in 0.2.0/0.3.0 (released today) and is consumed only by plugin-generated code — re-run npx expo prebuild after updating and the reference disappears. Bare-RN hosts following the old README snippet should simplify to the unconditional forward.

Verification

• expo prebuild regenerates the example AppDelegate with the docs-exact override; old generated blocks are migrated
• No references to the removed API remain in the repo

🤖 Generated with Claude Code