feat: add readme

README.md

@@ -1,2 +1,126 @@
 # U-Tad UI Project
 
+## Skill Tree System Implementation
+
+### Overview
+A complete skill tree system with node-based progression, prerequisite validation, visual connection lines, and data-driven configuration.
+
+---
+
+## Architecture: Blueprint Decision
+
+### Blueprint Implementation
+**Components:** `WBP_SkillTree`, `WBP_SkillNode`, `WBP_SkillNodeTooltip`
+
+**Reasoning:**
+- **Iteration speed**: UI layout and styling require rapid visual iteration
+- **Designer-friendly**: Artists/designers can modify UI without C++ knowledge
+
+---
+
+## Core Systems
+
+### 1. Data Layer (`SkillTreeTypes.h`)
+**Structures:**
+- `FSkillNodeData`: Skill definition row for skill data table (name, cost, prerequisites, effects, starting flag)
+- `FSkillNodeRuntime`: Runtime state wrapper
+- `ESkillNodeState`: State enum (Locked, Available, Selected, Purchased)
+
+**Decision**: Data Table-driven design allows non-programmers to configure skills without recompiling.
+
+### 2. Logic Layer (`SkillTreeComponent`)
+**Responsibilities:**
+- Skill tree initialization from DataTable
+- State management (prerequisites, affordability checks)
+- Selection validation and purchase confirmation
+- Starting skills auto-purchase
+- Skill point management
+- Effect application hooks
+
+**Key Features:**
+- **Purchase order sorting**: Ensures prerequisites are purchased before dependents
+- **Cascade deselection**: Removing a prerequisite deselects dependent skills
+- **Starting skills**: Marked in DataTable, auto-purchased at init, preserved on reset
+- **Stat aggregation**: Provides `GetTotal[Stat]Bonus()` functions to sum all purchased skills' bonuses
+
+### 3. Stats Integration Layer (`CharacterStatsComponent`)
+**Responsibilities:**
+- Automatic stat calculation from purchased skills
+- Character stat management (Health, Damage, Speed)
+- Real-time updates when skills are purchased
+- Movement speed integration
+
+**How it works:**
+- Finds SkillTreeComponent on same actor at BeginPlay
+- Listens to `OnSkillPurchased` event
+- Iterates all purchased skills, sums flat + percentage bonuses
+- Applies formula: `FinalStat = Base + FlatBonus + (Base * PercentBonus / 100)`
+- Auto-updates CharacterMovementComponent speed
+- Broadcasts stat change events for UI updates
+
+**Decision**: Separate stats component keeps concerns separated - SkillTreeComponent handles progression, CharacterStatsComponent handles stat application. Makes both reusable independently.
+
+### 4. Visualization Layer (`SkillTreeConnectionsWidget`)
+**Responsibilities:**
+- Automatic line drawing between prerequisite nodes (You only need to place nodes in the UI!)
+- Dynamic line coloring based on skill states
+- Event-driven refresh on state changes
+
+**Technical Approach:**
+- **Generic search**: Works with any widget hierarchy so designers/artist are not limited when creating the skill tree widget (Canvas, Overlay, Grid)
+- **NativePaint override**: Direct Slate rendering for performance
+- **Delegate binding**: Auto-refreshes when skills change state
+
+**Decision**: Single self-contained widget eliminates manual line management and Blueprint complexity.
+
+### 5. UI Layer (Blueprints)
+**WBP_SkillNode & WBP_SkillNodeTooltip:**
+- Displays skill icon, state, cost
+- Handles click events (select/deselect)
+- Stores SkillID for runtime lookup
+- Custom tooltip support to display skill details
+- Real time state updates via event binding allows real-time visual feedback
+
+**WBP_SkillTree:**
+- Contains manually-placed skill nodes
+- References SkillTreeComponent
+- Hosts SkillTreeConnectionsWidget which draws lines between nodes automatically
+- Binds to component events for UI updates
+
+**Decision**: Manual node placement allows custom layouts (linear, radial, branching) per designer preference.
+
+---
+
+## Key Design Decisions
+
+### 1. Skill prerequisites in DataTable
+**Alternative**: Hard-coded in C++ or DataAssets references
+**Chosen**: DataTable array
+**Reason**: Designers can modify skill dependencies without programmer intervention and without recompiling
+
+### 2. Component vs Subsystem
+**Alternative**: Game Instance Subsystem
+**Chosen**: Actor Component
+**Reason**: Supports multiple skill trees per player (e.g., combat tree, crafting tree) and easier save/load integration
+
+### 3. Single Connections Widget
+**Alternative**: Individual line widgets per connection with manual management
+**Chosen**: One widget draws all lines automatically
+**Reason**: Eliminates array management, better performance, automatic coordinate handling
+
+### 4. Separate Stats Component
+**Alternative**: Apply stats directly in SkillTreeComponent
+**Chosen**: Separate CharacterStatsComponent
+**Reason**: Separation of concerns - SkillTreeComponent is reusable for any progression system, CharacterStatsComponent specifically handles character stats. Allows skill trees without stat bonuses, or stats without skill trees.
+
+---
+
+## Technical Highlights
+
+- **Event-driven architecture**: Component broadcasts state changes, UI responds automatically
+- **State machine validation**: Prevents invalid transitions (e.g., can't select locked skills)
+- **Automatic stat application**: CharacterStatsComponent listens to skill purchases, recalculates stats, applies to character
+- **Geometry-aware rendering**: Lines adapt to any widget positioning system
+- **Data-driven configuration**: Zero code changes and no need to compile for new skills or tree layouts
+- **Reset functionality**: Refunds non-starting skills, maintains starting points
+- **Modular design**: Skill progression, stats, and visualization are independent