Emit overlay identity and presentation parent on route_change - #49

Why

Manifest (visual app map) cannot nest overlays under the screen that opened them. Unnamed sheets collapsed to ModalBottomSheetRoute<void>, overlayKind called bottom sheets modal, and exploration screenshot suppression dropped overlay after-frames when there was no claimed tap.

This change is additive. fromRoute, route, and navigation keep their existing meaning. The SDK does not invent RouteSettings.name or product CTA copy.

What

On every route_change:

• Split identity: routeName / routeType / routeNamed (and matching from*)
• Closed overlayKind: page | sheet | dialog | popup | unknown (sheets are sheet, not modal)
• Overlay push presentation parent: presentedOver* (route immediately below on the same navigator) and hostPage* (walk down to overlayKind == page, then parent navigators)
• Bounded same-navigator routeStack (max 16, routeStackTruncated when trimmed)
• Copy causeTargetFingerprint / causeGesture from the claimed interaction at emit time (claim-time snapshots miss post-pointer-up target resolution)
• Bypass exploration screenshot suppression when causeEventId != null or overlayKind != page

Presentation parent and hostPage* are omitted on page pushes, pops, and when the observer never recorded the underlying page. The SDK does not invent /home.

Paywall → unnamed sheet

fromRoute          = /subscriptionPaywall
overlayKind        = sheet
presentedOverRoute = /subscriptionPaywall
hostPageRoute      = /home

Tests

• Unit coverage for mechanical overlay classification
• Widget coverage for named popup → unnamed sheet identity, presentation parent, routeStack, claimed cause fingerprint, and overlay capture under exploration suppression
• Collector mapper passthrough for the new fields (routeNamed: false included)
• Existing modal visual fixtures assert sheet / dialog kinds without inventing an unobserved host page

Package version is 0.8.13. Route-change schema version stays 2.

Full packages/tugboat suite: 376 tests passed.