fix(frontend): address all PR review concerns

- Fix 7px → 11px font-size on section headers in RecipePicker
- Extract shared slotActions.ts with UUID validation for planId/slotId/recipeId
- Load full recipe list in planner page load (was placeholder current-week slots)
- Update planner/+page.svelte to pass data.recipes as allRecipes to RecipePicker
- Update planner and recipes page.server.ts to use shared slot action helpers
- Fix planner page.server tests: add recipes mock for parallel GET load
- Update action tests to use valid UUIDs (were 'plan-1'/'r1' style strings)
- Add validation-path tests for blank/invalid input on all slot actions
- Add tests for recipes/+server.ts GET endpoint (DayPicker week navigation)

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

frontend/src/routes/(app)/planner/+page.svelte

@@ -10,7 +10,7 @@
 	import UndoBar from '$lib/planner/UndoBar.svelte';
 	import { prevWeek, nextWeek, getWeekStart, weekDays, formatDayLabel, formatDayAbbr, formatWeekRange } from '$lib/planner/week';
 
-	let { data, form = null }: { data: { weekPlan: any; varietyScore: any; weekStart: string }; form?: any } = $props();
+	let { data, form = null }: { data: { weekPlan: any; varietyScore: any; weekStart: string; recipes: any[] }; form?: any } = $props();
 
 	// Use UTC date string (YYYY-MM-DD) consistently
 	const today: string = new Date().toISOString().slice(0, 10);
@@ -263,7 +263,7 @@
 			dateLabel={formatDayLabel(selectedDay)}
 			currentVarietyScore={varietyScore?.score ?? 0}
 			suggestions={[]}
-			allRecipes={weekPlan?.slots?.map((s: any) => s.recipe).filter(Boolean) ?? []}
+			allRecipes={data.recipes}
 			onpick={handleRecipePick}
 		/>
 	</BottomSheet>
@@ -495,7 +495,7 @@
 						dateLabel={formatDayLabel(pickerDate)}
 						currentVarietyScore={varietyScore?.score ?? 0}
 						suggestions={[]}
-						allRecipes={weekPlan?.slots?.map((s: any) => s.recipe).filter(Boolean) ?? []}
+						allRecipes={data.recipes}
 						onpick={handleRecipePick}
 					/>
 				</div>