Refactor skill allocation to upgrade; implement skill requirements and resource checks; remove experience from Pet model; update README for skill tree progress

README.md

@@ -1,28 +1,38 @@
 # Pet Companion
 
-## Todo:
-- [ ] Inventory system
-- [ ] Skill tree system
+## Todo (v1):
+- [P] Inventory system
+- [P] Skill tree system
 - [ ] Explore system
 - [ ] Battle system
-- [ ] Quest system
 - [ ] User login/register system
 - [ ] User profile/settings system
+
+### V1.5:
+- [ ]
+
+### V2:
+- [ ] Quest system
+- [ ] Market system (internal)
 - [ ] Front-End: 3D pet model
 - [ ] Front-End: 3D pet animations
 - [ ] Front-End: 3D pet interactions
 - [ ] Front-End: 3D pet environment (depending on the class)
 
+### V3:
+- [ ] Front-End: improved skill tree design
+- [ ] Front-End: improved inventory design
+
 ## Inventory system
-- [ ] Inventory UI
+- [x] Inventory UI
 - [x] Inventory database
 - [x] Inventory item database (items, consumables, equipment)
 - [x] Inventory item interactions (use, equip, unequip, drop)
 - [/] Inventory item stacking
-- [ ] Inventory item sorting (UI)
+- [/] Inventory item sorting (UI)
 
 ## Skill tree system
-- [ ] Skill tree UI
+- [x] Skill tree UI
 - [x] Skill tree database
 - [/] Skill tree interactions (learn, unlearn, upgrade)
 - [/] Skill tree requirements (level, skill points, other skills)