Beta hardening: expose isDebug + write real Render deprecation

[isaac-udy]

Summary

Two small beta-readiness items from the Tier-2 hardening list.

• isDebug is now a parameter on installNavigationController (and rememberNavigationController). The hardcoded internal val isDebug = false was a feature flag with no way to turn it on — the metadata-serializer validation it gates never ran in any real app. The processor now generates installNavigationController with an isDebug: Boolean = false parameter that's plumbed through internalCreateEnroController to set the flag on the controller before any module is added.

  MyComponent.installNavigationController(this, isDebug = BuildConfig.DEBUG)

  isDebug stays internal var on EnroController itself — it's not toggleable post-install — so the public API surface is just the install-time parameter.

• NavigationContainerState.Render deprecation now has a real message. The placeholder @Deprecated("TODO BETTER DEPRECATION MESSAGE") is replaced with proper text + ReplaceWith(NavigationDisplay(this)) — which is what Render was already delegating to internally.

Why

Both items would be embarrassing in a beta:

• isDebug was a feature flag with no way to turn it on. The serializer validation it controls is meant to surface missing serializers loudly in debug builds, but as shipped it was permanently off.
• The placeholder deprecation message would be visible in users' IDEs as a literal TODO string.

What's NOT in this PR

• SyntheticDestinationScope completeness — the bigger Tier-2 item that needs to collect operations during the block and integrate with the result-channel system. Wants design discussion and a focused PR.
• enro-compat removal plan — product decision, not code.
• Test-fixture TODO() calls in NavigationPathBindingTests — turned out to be a false alarm; they're intentional placeholders for deserialize/serialize lambdas that aren't exercised in tests that only check matches().

Test plan

• ./gradlew :enro-runtime:desktopTest — green, no regressions.
• ./gradlew :tests:application:compileKotlinDesktop — test app compiles against the new generated install signature.
• Inspect tests/application/build/generated/ksp/desktop/.../TestApplicationComponentNavigation.kt — confirm installNavigationController and rememberNavigationController both take and forward isDebug.
• Spot-check: IDE shows the real deprecation message on NavigationContainerState.Render() usage.

🤖 Generated with Claude Code