feat: add checkbox to include consumption from today until planner start date (#98)

- Add 'Include consumption from today until start date' checkbox to planner
- When checked, usage calculation starts from today instead of max(today, startDate)
- Persist checkbox state in localStorage per user
- Add i18n translations (EN + DE)
- Update planner tests to use dynamic future dates

frontend/src/styles.css

@@ -2019,6 +2019,25 @@ textarea.auto-resize {
 	text-transform: uppercase;
 	letter-spacing: 0.04em;
 }
+.planner-checkbox {
+	grid-column: 1 / -1;
+	display: flex;
+	flex-direction: row;
+	align-items: center;
+	gap: 0.75rem;
+	color: var(--text-secondary);
+	font-size: 0.875rem;
+	font-weight: 400;
+	text-transform: none;
+	letter-spacing: normal;
+	cursor: pointer;
+}
+.planner-checkbox input[type="checkbox"] {
+	width: 1.125rem;
+	height: 1.125rem;
+	cursor: pointer;
+	accent-color: var(--accent-primary);
+}
 .planner-actions {
 	grid-column: 1 / -1;
 	display: flex;