Adds work hours management with day-specific overrides

Introduces work hours management with weekly default and date-specific overrides to support per-column scheduling.

Calculates and applies non-work hour overlays to columns.
This allows users to visualize working and non-working times.

Adjusts event rendering to prevent overlap with horizontal timelines.

src/managers/WorkHoursManager.ts

@@ -0,0 +1,160 @@
+// Work hours management for per-column scheduling
+
+import { DateCalculator } from '../utils/DateCalculator';
+import { CalendarConfig } from '../core/CalendarConfig';
+
+/**
+ * Work hours for a specific day
+ */
+export interface DayWorkHours {
+  start: number; // Hour (0-23)
+  end: number;   // Hour (0-23)
+}
+
+/**
+ * Work schedule configuration
+ */
+export interface WorkScheduleConfig {
+  weeklyDefault: {
+    monday: DayWorkHours | 'off';
+    tuesday: DayWorkHours | 'off';
+    wednesday: DayWorkHours | 'off';
+    thursday: DayWorkHours | 'off';
+    friday: DayWorkHours | 'off';
+    saturday: DayWorkHours | 'off';
+    sunday: DayWorkHours | 'off';
+  };
+  dateOverrides: {
+    [dateString: string]: DayWorkHours | 'off'; // YYYY-MM-DD format
+  };
+}
+
+/**
+ * Manages work hours scheduling with weekly defaults and date-specific overrides
+ */
+export class WorkHoursManager {
+  private config: CalendarConfig;
+  private dateCalculator: DateCalculator;
+  private workSchedule: WorkScheduleConfig;
+
+  constructor(config: CalendarConfig) {
+    this.config = config;
+    this.dateCalculator = new DateCalculator(config);
+    
+    // Default work schedule - will be loaded from JSON later
+    this.workSchedule = {
+      weeklyDefault: {
+        monday: { start: 9, end: 17 },
+        tuesday: { start: 9, end: 17 },
+        wednesday: { start: 9, end: 17 },
+        thursday: { start: 9, end: 17 },
+        friday: { start: 9, end: 15 },
+        saturday: 'off',
+        sunday: 'off'
+      },
+      dateOverrides: {
+        '2025-01-20': { start: 10, end: 16 },
+        '2025-01-21': { start: 8, end: 14 },
+        '2025-01-22': 'off'
+      }
+    };
+  }
+
+  /**
+   * Get work hours for a specific date
+   */
+  getWorkHoursForDate(date: Date): DayWorkHours | 'off' {
+    const dateString = this.dateCalculator.formatISODate(date);
+    
+    // Check for date-specific override first
+    if (this.workSchedule.dateOverrides[dateString]) {
+      return this.workSchedule.dateOverrides[dateString];
+    }
+    
+    // Fall back to weekly default
+    const dayName = this.getDayName(date);
+    return this.workSchedule.weeklyDefault[dayName];
+  }
+
+  /**
+   * Get work hours for multiple dates (used by GridManager)
+   */
+  getWorkHoursForDateRange(dates: Date[]): Map<string, DayWorkHours | 'off'> {
+    const workHoursMap = new Map<string, DayWorkHours | 'off'>();
+    
+    dates.forEach(date => {
+      const dateString = this.dateCalculator.formatISODate(date);
+      const workHours = this.getWorkHoursForDate(date);
+      workHoursMap.set(dateString, workHours);
+    });
+    
+    return workHoursMap;
+  }
+
+  /**
+   * Calculate CSS custom properties for non-work hour overlays (before and after work)
+   */
+  calculateNonWorkHoursStyle(workHours: DayWorkHours | 'off'): { beforeWorkHeight: number; afterWorkTop: number } | null {
+    if (workHours === 'off') {
+      return null; // Full day will be colored via CSS background
+    }
+    
+    const gridSettings = this.config.getGridSettings();
+    const dayStartHour = gridSettings.dayStartHour;
+    const dayEndHour = gridSettings.dayEndHour;
+    const hourHeight = gridSettings.hourHeight;
+    
+    // Before work: from day start to work start
+    const beforeWorkHeight = (workHours.start - dayStartHour) * hourHeight;
+    
+    // After work: from work end to day end
+    const afterWorkTop = (workHours.end - dayStartHour) * hourHeight;
+    
+    return { 
+      beforeWorkHeight: Math.max(0, beforeWorkHeight), 
+      afterWorkTop: Math.max(0, afterWorkTop) 
+    };
+  }
+
+  /**
+   * Calculate CSS custom properties for work hours overlay (legacy - for backward compatibility)
+   */
+  calculateWorkHoursStyle(workHours: DayWorkHours | 'off'): { top: number; height: number } | null {
+    if (workHours === 'off') {
+      return null;
+    }
+    
+    const gridSettings = this.config.getGridSettings();
+    const dayStartHour = gridSettings.dayStartHour;
+    const hourHeight = gridSettings.hourHeight;
+    
+    const top = (workHours.start - dayStartHour) * hourHeight;
+    const height = (workHours.end - workHours.start) * hourHeight;
+    
+    return { top, height };
+  }
+
+  /**
+   * Load work schedule from JSON (future implementation)
+   */
+  async loadWorkSchedule(jsonData: WorkScheduleConfig): Promise<void> {
+    this.workSchedule = jsonData;
+  }
+
+  /**
+   * Get current work schedule configuration
+   */
+  getWorkSchedule(): WorkScheduleConfig {
+    return this.workSchedule;
+  }
+
+  /**
+   * Convert Date to day name key
+   */
+  private getDayName(date: Date): keyof WorkScheduleConfig['weeklyDefault'] {
+    const dayNames: (keyof WorkScheduleConfig['weeklyDefault'])[] = [
+      'sunday', 'monday', 'tuesday', 'wednesday', 'thursday', 'friday', 'saturday'
+    ];
+    return dayNames[date.getDay()];
+  }
+}