feat(planner): add remove meal with undo; fix RecipePicker badge for neutral delta

- MealActionSheet: new onremove prop + Entfernen button (guarded by #if)
- +page.svelte: handleRemoveMeal submits delete form, shows undo bar;
  undo re-adds via addSlot form; refactored handleUndo to undoCallback
  pattern; desktop day-detail panel also gets Entfernen button
- RecipePicker: only show green +delta badge when scoreDelta > 0;
  neutral (scoreDelta = 0) shows no badge instead of ⚠ Variationskonflikt
- Tests: page.test.ts remove-meal describe, RecipePicker neutral badge test

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

frontend/src/lib/planner/RecipePicker.svelte

@@ -104,7 +104,7 @@
 							{meta}
 						</p>
 					{/if}
-					{#if !suggestion.hasConflict}
+					{#if (suggestion.scoreDelta ?? 0) > 0}
 						<span
 							data-testid="badge-{suggestion.recipe.id}"
 							data-type="good"
@@ -112,7 +112,7 @@
 						>
 							↑ +{(suggestion.scoreDelta ?? 0).toFixed(1)} Punkte
 						</span>
-					{:else}
+					{:else if suggestion.hasConflict}
 						<span
 							data-testid="badge-{suggestion.recipe.id}"
 							data-type="warning"