fix: list every meal that a shopping trip buys for in the PDF

[guplem]

The shopping PDF dropped meals from the "Needed for" list of items that keep long. With the bundled defaults, trip 1 bought 28 eggs but listed only the 8 eggs of week 1. The meals of weeks 2 and 3 appeared on no page.

Cause

The PDF assumed that a trip buys only the weeks up to the next trip (_weeksByTrip). The planner puts an item that keeps on an earlier trip, also for later weeks (ADR 0014, 0015). So the trip that bought the item listed only its own week, and the later trips did not buy it at all. The same rule also chose the "Recommended" product from the wrong cooking events.

Fix

• TripItem.cookDays: the planner records the cook days that each trip item buys.
• IngredientMealRequirement.cookDayIndex replaces the stored cookWeekIndex, which is now a getter. The model is never saved to a file.
• buildShoppingPdfDocument puts each meal and each ranking event under the trip whose items hold its cook day. A meal that the owned stock covers goes under the first trip that buys the ingredient, because the list shows the whole need.
• ADR 0014 now states the day rule.

Result on the bundled defaults (trip 1)

Item	Bought	Listed before	Listed now
Huevo	28 pieces	8 pieces	28 pieces (weeks 1 to 3)
Aceite de Oliva	34 cl	10 meals	28 meals
Pimienta	32 grams	4 meals	12 meals

Tests

• Red-green TDD. A test with the real planner reproduced the bug first. New tests cover the planner cook days, the requirement cook day, and the owned-stock case.
• I reverted each rule once, and the matching test failed.
• 1053 tests pass, flutter analyze is clean, and the format check passes.

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