fix(docs): correct the Observation 'frozen' claim - the dataclass is frozen at the top level but the inner per-combatant/pair dicts are mutable copies; wording softened in the docstring and README (deep-freeze rejected: it would change the LLM contract and require touching pinned observation tests; copies are never read back by the engine, so policy mutation is already inert)

src/pf1e_simulator/combat.py

@@ -929,8 +929,11 @@ class Observation:
 
     Built by the engine at the point of policy invocation; the snapshot is the
     ONLY source of information for an ``LLMPolicy`` — it never exposes
-    ``engine.*`` callables nor mutable references to live state. All collections
-    are copied (tuples/dicts) so the snapshot is frozen and JSON-serializable.
+    ``engine.*`` callables nor mutable references to live state. All
+    collections are copies (tuples/dicts), never read back by the engine, so a
+    policy may mutate them freely without touching combat; the snapshot is
+    JSON-serializable (the top level is a frozen dataclass; the inner dicts are
+    plain mutable copies, not deep-frozen).
 
     ``combatants`` holds one dict per combatant in ``self._states`` order;
     ``pairs`` holds one dict per (acting combatant x each other combatant) with