Implement RFC 5545-compliant calendar system with v2 API

This major refactor eliminates manual string parsing throughout the
codebase and introduces proper RFC 5545 iCalendar specification
compliance with significant code simplification benefits.

## Backend Improvements
- Add complete RFC 5545-compliant data structures (VEvent, VTodo, etc.)
- Create simplified v2 API endpoints with direct DateTime support
- Eliminate ~150 lines of manual string parsing in handlers
- Add structured attendee and alarm support
- Maintain backward compatibility with existing v1 APIs

## Frontend Improvements
- Replace 16+ parameter create_event calls with single structured request
- Add automatic date/time conversion in EventCreationData
- Eliminate enum-to-string conversions throughout event creation
- Add v2 API models with proper type safety

## Technical Benefits
- Direct DateTime<Utc> usage instead of error-prone string parsing
- Proper RFC 5545 compliance with DTSTAMP, SEQUENCE fields
- Vec<AttendeeV2> instead of comma-separated strings
- Structured alarm system with multiple reminder types
- Enhanced RRULE support for complex recurrence patterns

## Code Quality
- Reduced create_event call from 16 parameters to 1 structured request
- Added comprehensive integration plan documentation
- Both backend and frontend compile successfully
- Maintained full backward compatibility during transition

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

integration_plan.md

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+# RFC 5545 Integration Plan
+
+## Phase 1: Core Structure Replacement (High Impact, Low Risk)
+
+### 1.1 Replace Event Models
+**Files to Update:**
+- `backend/src/calendar.rs` - Replace `CalendarEvent` with `VEvent`
+- `src/services/calendar_service.rs` - Replace `CalendarEvent` with `VEvent`
+- Remove duplicate structures, use single source of truth
+
+**Benefits:**
+- ✅ Eliminate duplicate event definitions
+- ✅ Add missing DTSTAMP (RFC required)
+- ✅ Add SEQUENCE for proper versioning
+- ✅ Standardize on DateTime<Utc> instead of string parsing
+
+### 1.2 Simplify Request/Response Models
+**Files to Update:**
+- `backend/src/models.rs` - Replace string-based fields
+
+**Current (Complex):**
+```rust
+pub start_date: String,        // YYYY-MM-DD format
+pub start_time: String,        // HH:MM format  
+pub categories: String,        // comma-separated
+pub attendees: String,         // comma-separated
+```
+
+**New (Simple):**
+```rust
+pub dtstart: DateTime<Utc>,
+pub categories: Vec<String>,
+pub attendees: Vec<Attendee>,
+```
+
+**Benefits:**
+- ✅ Remove ~50 lines of manual string parsing in handlers
+- ✅ Better type safety
+- ✅ Automatic validation
+
+## Phase 2: Enhanced Functionality (Medium Impact, Medium Risk)
+
+### 2.1 Add Rich Attendee Support
+**Current:** `Vec<String>` (just emails)
+**New:** `Vec<Attendee>` with roles, status, RSVP
+
+**Benefits:**
+- ✅ Proper meeting invitations
+- ✅ RSVP tracking
+- ✅ Role-based permissions (Chair, Required, Optional)
+
+### 2.2 Structured Reminders/Alarms
+**Current:** Simple reminder minutes
+**New:** Full `VAlarm` component with actions, triggers
+
+**Benefits:**
+- ✅ Multiple reminder types (email, display, audio)
+- ✅ Complex trigger patterns
+- ✅ Better CalDAV compatibility
+
+### 2.3 Geographic Location Support
+**New Addition:** `GEO` property for latitude/longitude
+
+**Benefits:**
+- ✅ Map integration possibilities
+- ✅ Location-based reminders
+- ✅ Travel time calculations
+
+## Phase 3: Advanced Components (High Impact, Higher Risk)
+
+### 3.1 Add VTODO Support
+**New Component:** Task/To-Do management
+
+**Benefits:**
+- ✅ Unified calendar + task system
+- ✅ Due dates, completion tracking
+- ✅ Priority management
+
+### 3.2 Add VJOURNAL Support
+**New Component:** Journal/diary entries
+
+**Benefits:**
+- ✅ Meeting notes integration
+- ✅ Daily journaling
+- ✅ Full calendar suite
+
+### 3.3 Add VFREEBUSY Support
+**New Component:** Availability tracking
+
+**Benefits:**
+- ✅ Meeting scheduling optimization
+- ✅ Conflict detection
+- ✅ Resource booking
+
+## Implementation Strategy
+
+### Immediate Actions (Can Start Now)
+1. **Add compatibility layer** in existing `CalendarEvent` to support new fields
+2. **Implement conversion functions** between old/new structures
+3. **Update backend models** to use DateTime instead of string parsing
+
+### Quick Wins (1-2 hours each)
+1. **Replace string date parsing** in `backend/src/handlers.rs`
+2. **Add missing DTSTAMP** to all events (RFC compliance)
+3. **Convert categories/attendees** from comma-separated strings to vectors
+
+### Medium Effort (3-5 hours each)
+1. **Unified event structure** across frontend/backend
+2. **Rich attendee management** with roles and status
+3. **Structured alarm system**
+
+### Long Term (Future enhancements)
+1. **Full VTODO implementation**
+2. **VJOURNAL support**
+3. **VFREEBUSY and scheduling**
+
+## Risk Mitigation
+
+### Backward Compatibility
+- Keep existing API endpoints working
+- Add conversion functions between old/new formats
+- Gradual migration, not big-bang replacement
+
+### Testing Strategy
+- Add tests for RFC 5545 compliance
+- Test CalDAV interoperability
+- Validate against multiple calendar clients
+
+### Rollback Plan
+- Keep old structures as fallback
+- Feature flags for new functionality
+- Incremental deployment
+
+## Expected Benefits
+
+### Developer Experience
+- **50% reduction** in date/time parsing code
+- **Elimination** of string-based field parsing
+- **Type safety** for all calendar operations
+- **Standards compliance** reduces debugging
+
+### User Experience
+- **Better CalDAV compatibility** with all clients
+- **Rich attendee management** for meetings
+- **Proper timezone handling**
+- **Future-proof** for advanced features
+
+### Maintenance
+- **Single source of truth** for event data
+- **RFC 5545 compliance** eliminates compatibility issues
+- **Cleaner codebase** with less duplication
+- **Easier testing** with structured data
+
+## File Impact Analysis
+
+### High Impact Files (Need Updates)
+```
+backend/src/models.rs       - Replace request/response structs
+backend/src/handlers.rs     - Remove string parsing logic
+backend/src/calendar.rs     - Replace CalendarEvent
+src/services/calendar_service.rs - Use unified structures
+```
+
+### Medium Impact Files (Minor Changes)
+```
+src/components/create_event_modal.rs - Update form handling
+src/components/event_modal.rs        - Display enhancements
+backend/src/lib.rs                   - Add new modules
+```
+
+### Low Impact Files (Minimal/No Changes)
+```
+src/components/week_view.rs   - Just use new event structure
+src/components/month_view.rs  - Just use new event structure
+styles.css                   - No changes needed
+```
+
+## Next Steps
+
+1. **Review this plan** with team/stakeholders
+2. **Create branch** for RFC 5545 integration
+3. **Start with Phase 1.1** - Core structure replacement
+4. **Implement conversion functions** for compatibility
+5. **Update one handler at a time** to reduce risk
+
+The integration will significantly simplify the codebase while adding professional-grade calendar functionality!