feat: complete core gameplay mechanics and structure without bonuses

- Implement Entity interface and base Player/Enemy abstract classes
- Implement Knight with Rule of Five combat actions and mana mechanics
- Add Skeleton with resurrect capability and key-drop logic
- Setup Location graph and Main game loop for turn-based combat
- Add comprehensive project README.md

.idea/misc.xml

@@ -8,7 +8,7 @@
       </list>
     </option>
   </component>
-  <component name="ProjectRootManager" version="2" project-jdk-name="25" project-jdk-type="JavaSDK">
+  <component name="ProjectRootManager" version="2" languageLevel="JDK_25" project-jdk-name="homebrew-26" project-jdk-type="JavaSDK">
     <output url="file://$PROJECT_DIR$/out" />
   </component>
 </project>