fix: scope import ViewModel per-uri so a second import re-parses

ImportScreen has no nav backstack, so an unkeyed hiltViewModel() resolved
to the Activity's ViewModelStore and was retained across imports. Its
one-shot `load` guard then showed the *previous* file's parsed state on
the next import — trivially reachable now that the in-app Restore button
lets you export→restore or restore twice in one session (worst case: the
picker still holds file A, so tapping Import writes A's events after you
picked B). Keying the VM by the file uri hands each distinct file a fresh
VM (fresh Loading state); the same uri (rotation) reuses it and holds the
result.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/java/de/jeanlucmakiola/calendula/ui/imports/ImportScreen.kt

@@ -75,7 +75,13 @@ fun ImportScreen(
     onClose: () -> Unit,
     onOpenSingle: (EventForm) -> Unit,
     forceMany: Boolean = false,
-    viewModel: ImportViewModel = hiltViewModel(),
+    // Key the VM by the file uri. This screen has no nav backstack, so an
+    // unkeyed hiltViewModel() resolves to the Activity's store and is retained
+    // across imports — its one-shot `load` guard would then show the *previous*
+    // file's parsed state on the next import (a second restore, export→restore,
+    // etc.). Keying per uri hands each distinct file a fresh VM (fresh Loading
+    // state), while the same uri (rotation) reuses it and holds the result.
+    viewModel: ImportViewModel = hiltViewModel(key = uri.toString()),
 ) {
     LaunchedEffect(uri) { viewModel.load(uri, forceMany) }
     val state by viewModel.state.collectAsStateWithLifecycle()