feat: Implement dose calculation fix and enhance legend feature

- Fixed dose calculation logic in `_calculate_daily_dose` to correctly parse timestamps with multiple colons.
- Added comprehensive test cases for various dose formats and edge cases in `test_dose_calculation.py`.
- Enhanced graph legend to display individual medicines with average dosages and track medicines without dose data.
- Updated legend styling and positioning for better readability and organization.
- Created new tests for enhanced legend functionality, including handling of medicines with and without data.
- Improved mocking for matplotlib components in tests to prevent TypeErrors.

ENHANCED_LEGEND_FEATURE.md

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+# Enhanced Graph Legend Feature
+
+## Overview
+Expanded the graph legend to display each medicine individually with enhanced formatting and additional information about tracked medicines.
+
+## Changes Made
+
+### 1. Enhanced Legend Display (`src/graph_manager.py`)
+
+#### Legend Formatting Improvements:
+- **Multi-column Layout**: Legend now displays in 2 columns for better space usage
+- **Improved Positioning**: Positioned at upper left with proper bbox anchoring
+- **Enhanced Styling**: Added frame, shadow, and transparency for better readability
+- **Font Optimization**: Uses smaller font size to fit more information
+
+#### Medicine-Specific Information:
+- **Average Dosage Display**: Each medicine shows average dosage in the legend
+  - Format: `"Bupropion (avg: 125.5mg)"`
+  - Calculated from all days with non-zero doses
+- **Color-Coded Entries**: Each medicine maintains its distinct color in the legend
+- **Tracked Medicine Indicator**: Shows medicines that are toggled on but have no dose data
+
+### 2. Legend Configuration Details
+
+```python
+self.ax.legend(
+    handles,
+    labels,
+    loc='upper left',           # Position
+    bbox_to_anchor=(0, 1),      # Anchor point
+    ncol=2,                     # 2 columns
+    fontsize='small',           # Compact text
+    frameon=True,               # Show frame
+    fancybox=True,              # Rounded corners
+    shadow=True,                # Drop shadow
+    framealpha=0.9              # Semi-transparent background
+)
+```
+
+### 3. Data Tracking Enhancements
+
+#### Medicine Categorization:
+- **`medicines_with_data`**: Medicines with actual dose recordings
+- **`medicines_without_data`**: Medicines toggled on but without dose data
+
+#### Average Calculation:
+```python
+total_medicine_dose = sum(daily_doses)
+non_zero_doses = [d for d in daily_doses if d > 0]
+avg_dose = total_medicine_dose / len(non_zero_doses)
+```
+
+## Features
+
+### Enhanced Legend Display:
+✅ **Multi-column Layout**: Efficient use of graph space
+✅ **Medicine-Specific Info**: Average dosage displayed for each medicine
+✅ **Color Coding**: Consistent color scheme for easy identification
+✅ **Tracked Medicine Status**: Shows which medicines are being monitored
+✅ **Professional Styling**: Frame, shadow, and transparency effects
+
+### Information Provided:
+- **Symptom Data**: Depression, Anxiety, Sleep, Appetite with descriptive labels
+- **Medicine Doses**: Each medicine with average dosage calculation
+- **Tracking Status**: Indication of medicines being tracked but without current dose data
+- **Visual Consistency**: Color-coded entries matching the graph elements
+
+### Example Legend Entries:
+```
+Depression (0:good, 10:bad)     Sleep (0:bad, 10:good)
+Anxiety (0:good, 10:bad)        Appetite (0:bad, 10:good)
+Bupropion (avg: 225.0mg)        Propranolol (avg: 12.5mg)
+Tracked (no doses): hydroxyzine, gabapentin
+```
+
+## Benefits
+
+### For Users:
+- **Clear Identification**: Easy to see which medicines are displayed and their average doses
+- **Data Context**: Understanding of dosage patterns at a glance
+- **Tracking Awareness**: Knowledge of which medicines are being monitored
+- **Professional Appearance**: Clean, organized legend that doesn't clutter the graph
+
+### For Analysis:
+- **Quick Reference**: Average doses visible without calculation
+- **Pattern Recognition**: Color coding helps identify medicine effects
+- **Data Completeness**: Clear indication of missing vs. present data
+- **Visual Organization**: Structured layout for easy reading
+
+## Technical Implementation
+
+### Legend Components:
+1. **Handles and Labels**: Retrieved from current plot elements
+2. **Additional Info**: Dynamically added for medicines without data
+3. **Dummy Handles**: Invisible rectangles for text-only legend entries
+4. **Formatting**: Applied consistently across all legend elements
+
+### Positioning Logic:
+- **Upper Left**: Avoids interference with data plots
+- **2-Column Layout**: Maximizes information density
+- **Responsive**: Adjusts to available content
+
+The enhanced legend provides comprehensive information about all displayed elements while maintaining a clean, professional appearance that enhances the overall user experience.