fix(calendar): keep declaration-entry months fixed while editing

Declaring a date at the edge of the planning period widened the
projection and inserted a disabled month above the grid. Declaration
entry now lists only the planning period's months, while selections
keep the connected-period widening.

Refs #276

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/components/calendar-year/calendar-year.ts

@@ -272,11 +272,10 @@ export class CalendarYear {
 		const horizon = this.calendarHorizon();
 		if (!horizon) return undefined;
 		if (this.declarationEntry())
-			return this.calendarService.project({
-				placements: [],
-				horizon,
-				declaredDays: this.userInput.declaredDaysSignal(),
-			});
+			return this.calendarService.project(
+				{ placements: [], horizon, declaredDays: this.userInput.declaredDaysSignal() },
+				{ fixedMonths: true },
+			);
 		const plan = this.displayedPlan();
 		return this.calendarService.project(
 			plan ? { ...plan, horizon: plan.horizon ?? horizon } : { placements: [], horizon },