Implement storage widget tree structure with themed status icons

Add proper hierarchical tree display for storage pools and drives:
- Pool headers with status icons and type indication (Single/multi-drive)
- Individual drive lines with ├─ tree symbols and health status
- Usage summary with └─ end symbol and capacity status
- T: and W: prefixes for temperature and wear level metrics
- Themed status icons using StatusIcons::get_icon() with proper colors
- 2-space indentation for clean tree structure appearance

Replace flat storage display with beautiful tree format:
● Storage steampool (multi-drive):
  ├─ ● sdb T:35°C W:12%
  ├─ ● sdc T:38°C W:8%
  └─ ● 78.1% 1250.3GB/1600.0GB

Uses agent-calculated status from NixOS-configured thresholds.
Update CLAUDE.md with complete implementation specification.

CLAUDE.md

@@ -397,6 +397,43 @@ Agent → ["cpu_load_1min", "memory_usage_percent", ...] → Dashboard → Widge
 - [x] Eliminated configuration drift between defaults and deployed settings
 - [x] All cm-dashboard configuration now managed declaratively through NixOS
 
+**In Progress:**
+- [ ] **Storage Widget Tree Structure Implementation (2025-10-22)**
+- [ ] Replace flat storage display with proper tree structure format
+- [ ] Implement themed status icons for pool/drive/usage status
+- [ ] Add tree symbols (├─, └─) with proper indentation for hierarchical display
+- [ ] Support T: and W: prefixes for temperature and wear metrics
+- [ ] Use agent-calculated status from NixOS-configured thresholds (no dashboard calculations)
+
+### Storage Widget Tree Structure Specification
+
+**Target Display Format:**
+```
+● Storage steampool (Raid0):
+  ├─ ● sdb T:35°C W:12%
+  ├─ ● sdc T:38°C W:8%
+  └─ ● 78.1% 1250.3GB/1600.0GB
+```
+
+**Status Icon Sources:**
+- **Pool Status**: Aggregated status from pool health + usage (`disk_{pool}_usage_percent` metric status)
+- **Drive Status**: Individual SMART health status (`disk_{pool}_{drive}_health` metric status)  
+- **Usage Status**: Disk usage level status (`disk_{pool}_usage_percent` metric status)
+
+**Implementation Details:**
+- **Tree Symbols**: `├─` for intermediate lines, `└─` for final line
+- **Indentation**: 2 spaces before tree symbols
+- **Status Icons**: Use `StatusIcons::get_icon(status)` with themed colors
+- **Temperature Format**: `T:{temp}°C` from `disk_{pool}_{drive}_temperature` metrics
+- **Wear Format**: `W:{wear}%` from `disk_{pool}_{drive}_wear_percent` metrics  
+- **Pool Type**: Determine from drive count (Single/multi-drive) or RAID type detection
+- **Status Calculation**: Dashboard displays agent-calculated status, no threshold evaluation
+
+**Layout Constraints:**
+- Dynamic: 1 header + N drives + 1 usage line per storage pool
+- Supports multiple storage pools with proper spacing
+- Truncation indicator if pools exceed available display space
+
 **Production Configuration:**
 - CPU load thresholds: Warning ≥ 9.0, Critical ≥ 10.0
 - CPU temperature thresholds: Warning ≥ 100°C, Critical ≥ 100°C (effectively disabled)