feat(android-nav3): [Android Nav3 3] Track navigation state transitions

[0xadam-brown]

PR Stack (Android Nav3)

• feat(android-nav3): Android Nav3 integration #6105
• feat(android-nav3): [Android Nav3 1] Create the navigation3 module #6106
• feat(android-nav3): [Android Nav3 2] Model navigation routes #6107
• feat(android-nav3): [Android Nav3 3] Track navigation state transitions #6108
• feat(android-nav3): [Android Nav3 4] Introduce SentryNavEffect #6109

---

📜 Description

Add the observer layer for Android Nav3.

This PR teaches the module how to interpret Navigation 3 back stack changes as Sentry state
transitions: breadcrumbs, screen context, back stack context, and route-scoped navigation
transactions.

💡 Motivation and Context

With route modeling in place, the next boundary is the state machine that reacts to navigation
changes. Keeping that behavior separate makes it easier to review lifecycle and tracing semantics
without mixing in Compose effect concerns yet.

💚 How did you test it?

• ./gradlew :sentry-android-navigation3:testReleaseUnitTest
• ./gradlew spotlessApply
• ./gradlew apiDump

📝 Checklist

• I added GH Issue ID & Linear ID
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• I updated the wizard if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.
• Public API changes reviewed by another Mobile SDK team member or implemented according to the develop docs spec.

🔮 Next steps

Introduce the Compose-facing effect that owns this observer in application code.

#skip-changelog

⚠️ Merge this PR using a merge commit (not squash). Only the collection branch is squash-merged into main.

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Android

🔗 App Name	App ID	Version	Configuration
SDK Size	io.sentry.tests.size	8.56.0 (1)	release

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