fix(ui/navigation): pop the sheet entry when a drag dismisses it

[bmc08gt]

The bug

Drag a sheet that shows over the v2 tab bar closed (region selection from the wallet tab) and the tab bar doesn't come back — it stays hidden until you tap the screen, and that first tap is swallowed rather than doing what you aimed it at.

Root cause

UnstyledBottomSheet (compose-unstyled) has no dismissal callback. That wiring existed when the scene used Material3's ModalBottomSheet — its onDismissRequest popped the nav entry once a user drag settled the sheet to Hidden — and nothing replaced it when the scene was rebuilt on the unstyled sheet in 6e49a91.

So a drag-dismiss hides the sheet without telling anyone:

• the AppRoute.Main.Sheet(...) entry stays on the backstack, so navigator.currentRouteKey still resolves to the sheet → topTab == null → AppNavigationBar keeps the tab bar hidden;
• the scene's full-size scrim is still composed (just animated to alpha 0), so it eats every touch until one lands on its noRippleClickable { dismiss(true) }, which — seeing currentDetent == Hidden — pops immediately.

That is exactly the reported "doesn't show until you interact with the screen".

The fix

Watch the sheet's state instead of the gesture, so every dismissal route is covered rather than just the drag:

1. wait until the sheet has actually been presented (targetDetent != Hidden — targeted, not settled, so an interrupted open animation still counts);
2. then wait for it to settle back at Hidden (isIdle && currentDetent == Hidden — a conjunction, because a partial drag flips the target to Hidden and back as the finger crosses the threshold);
3. pop.

Both explicit dismiss paths (dismiss()'s animate-then-pop and the pendingSheetDismiss replace) now route through the same idempotent finishDismiss(), which the settle observer also calls — so the entry pops exactly once per presentation and can't take a second backstack entry with it. The guard resets on sheetGeneration, so a same-route dismiss-then-replace still re-arms.

Tests

New ModalBottomSheetSceneTest (Robolectric + compose test rule) — the drag case fails on the pre-fix code (expected:<1> but was:<0>) and passes after:

• dragging the sheet closed pops its entry
• an open sheet does not pop its entry — control, guards the eager/double-pop direction

Verified:

• :ui:navigation:testDebugUnitTest — 31 tests, 0 failures (existing CodeNavigator* and InnerFlowNavigator suites included)
• :apps:flipcash:core:testDebugUnitTest + :apps:flipcash:app:testDebugUnitTest — green