fix(#5): address PR review — share ExpandedFab, inject GetExpenseSummary, column-chart spec

- Add ui/components/ExpandedFab.kt with ExpandedFab + MiniFab helpers; HomeScreen and ExpenseListScreen both consume it, the tab-collapsing LaunchedEffect in ExpenseListScreen is hoisted to its Content()
- Inject GetExpenseSummary in HomeScreenModel; drive summary via dateRange.flatMapLatest { getExpenseSummary.await(it) } (fixes the period-filter total-card flicker) and drop the inline combine(expenses, dateRange) recomputation
- Hoist isFabExpanded out of HomeScreenModel into HomeScreen.Content() so the FAB state is local to the composable
- Convert HomeScreenModel.exportToCsv from a callback to a suspend fun returning Result<Unit>; the screen does the snackbar dispatch on the coroutineScope
- Consolidate DateRangeOption label mapping to a single DateRangeOption.labelRes() / .labelText() pair (one source of truth)
- Rename FAB string keys to shared fab_manual / fab_import and drop the home_fab_* duplicates
- Update docs/04-implementation-plan.md and .opencode/agent/implementor.md Charts sections to reflect the Vico 2.0.0 column-chart-with-legend substitution (Vico 2.0.0 has no pie layer)

.opencode/agent/implementor.md

@@ -217,7 +217,7 @@ class AppPreference(private val store: PreferenceStore) {
 ### Charts
 
 - **Vico** (`com.patrykandpatrick.vico:compose`, `compose-m3`, `core`) is the only charting library used.
-- `HomeScreen` dashboard renders a pie chart from `ExpenseSummary.byCategory` via Vico's `Chart` composable. No Canvas drawing for charts.
+- `HomeScreen` dashboard renders a Vico `ColumnCartesianLayer` (one bar per category) from `ExpenseSummary.byCategory`, with a small `Row { colored swatch; category name; amount }` legend below the chart that carries the per-category color. Vico 2.0.0's `cartesian` package only exposes `Line` / `Column` / `Candlestick` layers (no pie), so the dashboard uses a column chart with a legend; per-category colors live in the legend, not in the chart. No Canvas drawing for charts.
 - Apache 2.0 license, Compose-native, no AndroidView wrapper.
 
 ---
@@ -231,7 +231,7 @@ class AppPreference(private val store: PreferenceStore) {
 | Koin | 4.2.2 | DI |
 | Room | 2.7.1 | Local DB |
 | PDFBox-Android | 2.0.27.0 | PDF text extraction |
-| Vico (compose / compose-m3 / core) | 2.x | Charts (pie / bar) |
+| Vico (compose / compose-m3 / core) | 2.x | Charts (column with legend) |
 | Okio | (transitive) | CSV write |
 
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