feat(app): экраны импорта отчётов, целей, доходов, ребалансировки, налогов и бенчмарков

Импорт (/imports, /instruments/pending) и фаза 4 (/goals, /income,
/rebalance, /tax, аналитика-хаб с benchmarks_card) — по
docs/ai/import-contract.md и docs/ai/phase4-contract.md. file_picker для
загрузки отчёта.

app/lib/core/widgets/scope_selector.dart

@@ -0,0 +1,46 @@
+import 'package:fintracker_api/fintracker_api.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+import '../../features/portfolio/providers.dart';
+import 'async_value_view.dart';
+
+/// The `all | account:<id> | portfolio:<id>` selector, shared by every screen scoped the
+/// same way (Портфель, Доходы, Налоги). Hidden while there is nothing to choose between —
+/// a dropdown with one option is furniture, not a control.
+///
+/// It drives the app-wide [scopeProvider] on purpose: two screens showing different scopes
+/// at the same time is a trap, not a feature.
+class ScopeSelector extends ConsumerWidget {
+  const ScopeSelector({super.key});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final scopes = ref.watch(scopesProvider);
+    final current = ref.watch(scopeProvider);
+
+    return AsyncValueView<List<ScopeOut>>(
+      value: scopes,
+      data: (rows) {
+        if (rows.length < 2) return const SizedBox.shrink();
+        final known = rows.any((s) => s.scope == current) ? current : rows.first.scope;
+        return DropdownButtonHideUnderline(
+          child: DropdownButton<String>(
+            value: known,
+            borderRadius: BorderRadius.circular(8),
+            items: [
+              for (final s in rows)
+                DropdownMenuItem(
+                  value: s.scope,
+                  child: Text(s.name, overflow: TextOverflow.ellipsis),
+                ),
+            ],
+            onChanged: (value) {
+              if (value != null) ref.read(scopeProvider.notifier).state = value;
+            },
+          ),
+        );
+      },
+    );
+  }
+}

app/lib/core/widgets/section_card.dart

@@ -0,0 +1,89 @@
+import 'package:flutter/material.dart';
+
+/// A titled card section, the layout unit the phase-4 screens are built from (the same
+/// shape Портфель already uses inline).
+class SectionCard extends StatelessWidget {
+  const SectionCard({required this.title, required this.child, this.subtitle, this.trailing, super.key});
+
+  final String title;
+  final String? subtitle;
+  final Widget? trailing;
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return Card(
+      child: Padding(
+        padding: const EdgeInsets.all(16),
+        child: Column(
+          crossAxisAlignment: CrossAxisAlignment.start,
+          children: [
+            Row(
+              children: [
+                Expanded(
+                  child: Column(
+                    crossAxisAlignment: CrossAxisAlignment.start,
+                    children: [
+                      Text(title, style: theme.textTheme.titleMedium),
+                      if (subtitle != null)
+                        Padding(
+                          padding: const EdgeInsets.only(top: 2),
+                          child: Text(
+                            subtitle!,
+                            style: theme.textTheme.bodySmall?.copyWith(color: theme.hintColor),
+                          ),
+                        ),
+                    ],
+                  ),
+                ),
+                ?trailing,
+              ],
+            ),
+            const SizedBox(height: 12),
+            child,
+          ],
+        ),
+      ),
+    );
+  }
+}
+
+/// A compact labelled number, used for the summary rows of the phase-4 screens.
+class StatTile extends StatelessWidget {
+  const StatTile({required this.label, required this.value, this.note, this.width = 184, super.key});
+
+  final String label;
+  final Widget value;
+  final String? note;
+  final double width;
+
+  @override
+  Widget build(BuildContext context) {
+    final theme = Theme.of(context);
+    return SizedBox(
+      width: width,
+      child: Card(
+        child: Padding(
+          padding: const EdgeInsets.all(12),
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.start,
+            children: [
+              Text(label, style: theme.textTheme.bodySmall),
+              const SizedBox(height: 4),
+              DefaultTextStyle(style: theme.textTheme.titleMedium!, child: value),
+              if (note != null) ...[
+                const SizedBox(height: 2),
+                Text(
+                  note!,
+                  style: theme.textTheme.bodySmall?.copyWith(color: theme.hintColor),
+                  maxLines: 3,
+                ),
+              ],
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}