Initial commit: Complete CalDAV calendar synchronizer

- Rust-based CLI tool for Zoho to Nextcloud calendar sync
- Selective calendar import from Zoho to single Nextcloud calendar
- Timezone-aware event handling for next-week synchronization
- Comprehensive configuration system with TOML support
- CLI interface with debug, list, and sync operations
- Complete documentation and example configurations

config/default.toml

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+# Default CalDAV Sync Configuration
+# This file provides default values for the Zoho to Nextcloud calendar sync
+
+# Zoho Configuration (Source)
+[zoho]
+server_url = "https://caldav.zoho.com/caldav"
+username = ""
+password = ""
+selected_calendars = []
+
+# Nextcloud Configuration (Target)  
+[nextcloud]
+server_url = ""
+username = ""
+password = ""
+target_calendar = "Imported-Zoho-Events"
+create_if_missing = true
+
+[server]
+# Request timeout in seconds
+timeout = 30
+
+[calendar]
+# Calendar color in hex format
+color = "#3174ad"
+# Default timezone for processing
+timezone = "UTC"
+
+[sync]
+# Synchronization interval in seconds (300 = 5 minutes)
+interval = 300
+# Whether to perform synchronization on startup
+sync_on_startup = true
+# Number of weeks ahead to sync
+weeks_ahead = 1
+# Whether to run in dry-run mode (preview changes only)
+dry_run = false
+
+# Performance settings
+max_retries = 3
+retry_delay = 5
+
+# Optional filtering configuration
+# [filters]
+# # Event types to include (leave empty for all)
+# event_types = ["meeting", "appointment"]
+# # Keywords to filter events by
+# keywords = ["work", "meeting", "project"]
+# # Keywords to exclude
+# exclude_keywords = ["personal", "holiday", "cancelled"]
+# # Minimum event duration in minutes
+# min_duration_minutes = 5
+# # Maximum event duration in hours
+# max_duration_hours = 24

config/example.toml

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+# CalDAV Configuration Example
+# This file demonstrates how to configure Zoho and Nextcloud CalDAV connections
+# Copy and modify this example for your specific setup
+
+# Global settings
+global:
+  log_level: "info"
+  sync_interval: 300  # seconds (5 minutes)
+  conflict_resolution: "latest"  # or "manual" or "local" or "remote"
+  timezone: "UTC"
+
+# Zoho CalDAV Configuration (Source)
+zoho:
+  enabled: true
+  
+  # Server settings
+  server:
+    url: "https://caldav.zoho.com/caldav"
+    timeout: 30  # seconds
+  
+  # Authentication
+  auth:
+    username: "your-zoho-email@domain.com"
+    password: "your-zoho-app-password"  # Use app-specific password, not main password
+  
+  # Calendar selection - which calendars to import from
+  calendars:
+    - name: "Work Calendar"
+      enabled: true
+      color: "#4285F4"
+      sync_direction: "pull"  # Only pull from Zoho
+      
+    - name: "Personal Calendar"
+      enabled: true
+      color: "#34A853"
+      sync_direction: "pull"
+      
+    - name: "Team Meetings"
+      enabled: false  # Disabled by default
+      color: "#EA4335"
+      sync_direction: "pull"
+  
+  # Sync options
+  sync:
+    sync_past_events: false  # Don't sync past events
+    sync_future_events: true
+    sync_future_days: 7  # Only sync next week
+    include_attendees: false  # Keep it simple
+    include_attachments: false
+
+# Nextcloud CalDAV Configuration (Target)
+nextcloud:
+  enabled: true
+  
+  # Server settings
+  server:
+    url: "https://your-nextcloud-domain.com"
+    timeout: 30  # seconds
+  
+  # Authentication
+  auth:
+    username: "your-nextcloud-username"
+    password: "your-nextcloud-app-password"  # Use app-specific password
+  
+  # Calendar discovery
+  discovery:
+    principal_url: "/remote.php/dav/principals/users/{username}/"
+    calendar_home_set: "/remote.php/dav/calendars/{username}/"
+    
+  # Target calendar - all Zoho events go here
+  calendars:
+    - name: "Imported-Zoho-Events"
+      enabled: true
+      color: "#FF6B6B"
+      sync_direction: "push"  # Only push to Nextcloud
+      create_if_missing: true  # Auto-create if it doesn't exist
+  
+  # Sync options
+  sync:
+    sync_past_events: false
+    sync_future_events: true
+    sync_future_days: 7
+
+# Event filtering
+filters:
+  events:
+    exclude_patterns:
+      - "Cancelled:"
+      - "BLOCKED"
+    
+    # Time-based filters
+    min_duration_minutes: 5
+    max_duration_hours: 24
+    
+    # Status filters
+    include_status: ["confirmed", "tentative"]
+    exclude_status: ["cancelled"]
+
+# Logging
+logging:
+  level: "info"
+  format: "text"
+  file: "caldav-sync.log"
+  max_size: "10MB"
+  max_files: 3
+
+# Performance settings
+performance:
+  max_concurrent_syncs: 3
+  batch_size: 25
+  retry_attempts: 3
+  retry_delay: 5  # seconds
+
+# Security settings
+security:
+  ssl_verify: true
+  encryption: "tls12"