refactor(planner): export Slot and SlotMap from types.ts

Adds shared Slot and SlotMap interfaces so DesktopDayTile,
EmptyDayTile, and reasoningTags can import rather than re-declare.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/planner/types.ts

@@ -13,6 +13,14 @@ export interface Recipe {
 	tags?: TagItem[];
 }
 
+export interface Slot {
+	id?: string | null;
+	slotDate?: string;
+	recipe?: Recipe | null;
+}
+
+export type SlotMap = Record<string, Slot>;
+
 export interface Suggestion {
 	recipe: Recipe;
 	scoreDelta: number;