Add level 5: Chambers (dictionaries + lists)

Top-level `chambers:` mapping; each chamber name maps to an item list.
2-3 chambers, 2-3 items each, drawn from typed pools. Deterministic per
seed via ChaCha8Rng XOR'd with 0x..05.

Not wired into levels::registry() yet — integration belongs to a follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/levels/mod.rs

@@ -13,6 +13,7 @@
 pub mod l01_minimum;
 pub mod l02_kv;
 pub mod l03_dict;
+pub mod l05_dict_list;
 
 use serde::{Deserialize, Serialize};