docs: lifecycle events + openURL public API [rn] (4/4)

[choudlet]

Summary

Slice 4 of 4 in the RN lifecycle stack (sc-36800). README documentation for the feature landed in PRs 1-3.

Stacked on #36. Review the diff against that branch.

Coverage

• Lifecycle Events table — the four events with trigger conditions and emitted properties.
• Opt-in framing — `trackLifecycleEvents` default flipped to `false`, code sample for enabling, opt-in callout in the Features list.
• `openURL` public API — documented in the Analytics Interface section and a dedicated Deep-link wiring subsection with code samples (Linking forwarding, `sourceApplication` usage).
• Buffer semantics — one-shot, last-write-wins, cleared on emit, no-op + warning when disabled.
• Privacy & sanitization — worked example showing how a host can strip tokens / OTPs / magic-link secrets before forwarding (the SDK passes URLs verbatim).
• Why no auto-instrumentation — no swizzling, no AppDelegate proxy, host-controlled hand-off via `openURL` (avoids conflicts with Firebase / Branch / etc., respects privacy, gives hosts control).
• API Reference — `trackLifecycleEvents` default updated to `false`, Analytics Interface gains an `openURL` bullet.

Stack

1. #34 — storage foundation
2. #35 — emitter
3. #36 — client wiring + `openURL` + opt-in default
4. This PR — README documentation

Test plan

• Markdown renders cleanly on GitHub (table, code blocks, anchors)
• Internal anchor `#application-lifecycle-events` resolves from the TOC and from in-line cross-references