Support multiple pantry entries for the same ingredient with different expiry dates

Ones doesn't buy groceries only when the quantity completely depletes (eg. eggs).

Currently the WebUI and the CLI seems to not support multiple entries for the same ingredient in the same pantry category, it would be useful to track the same ingredient with multiple expiration dates.

**Tested conf:**
```
[fridge]
eggs = [{ quantity = "6", expire = "2026-04-25" }, { quantity = "4", expire = "2026-04-15" }]
```
**Expected result:** 2 eggs entries listed, one with 6 and the other with 4, with different expiration dates.
**Current result:** The entry is ignored.

The same ingredient in multiple categories is supported but I don't know how it behave regarding quantity computation for recipes. Indeed, each entry of the same ingredient (even in different categories) must add up.