fix: use nested .get() calls to handle falsy values correctly

Addresses Gemini Code Assist review feedback:
- Changed `or` fallbacks to nested `.get()` calls to avoid bugs with falsy values
- Empty dict `{}` for attributes is valid and should not fall back
- Empty string `''` for state is valid and should not fall back

The nested `.get(key1, .get(key2, default))` pattern only falls back when
the key is missing, not when the value is falsy, which is the correct behavior.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: julienld

src/ha_mcp/tools/tools_history.py

@@ -328,20 +328,20 @@ async def ha_get_history(
                         # Get timestamps - WebSocket returns short-form (lc/lu) as Unix epoch floats
                         # or long-form (last_changed/last_updated) as strings
                         # Note: HA WebSocket API omits 'lc' when it equals 'lu' (optimization)
-                        last_updated_raw = state.get("lu") or state.get("last_updated")
-                        last_changed_raw = state.get("lc") or state.get("last_changed")
+                        last_updated_raw = state.get("lu", state.get("last_updated"))
+                        last_changed_raw = state.get("lc", state.get("last_changed"))
 
                         # If last_changed is missing, it means it equals last_updated
                         if last_changed_raw is None and last_updated_raw is not None:
                             last_changed_raw = last_updated_raw
 
                         state_entry = {
-                            "state": state.get("s") or state.get("state"),
+                            "state": state.get("s", state.get("state")),
                             "last_changed": _convert_timestamp(last_changed_raw),
                             "last_updated": _convert_timestamp(last_updated_raw),
                         }
                         if not minimal_response:
-                            state_entry["attributes"] = state.get("a") or state.get("attributes", {})
+                            state_entry["attributes"] = state.get("a", state.get("attributes", {}))
                         formatted_states.append(state_entry)
 
                     entities_history.append(