style: apply cargo fmt to entire codebase

Standardize code formatting across all 173 Rust source files
using rustfmt. No functional changes - purely cosmetic.

This establishes a consistent code style baseline for the
project going forward.

src/application/dtos/calendar_dto.rs

@@ -1,8 +1,8 @@
-use serde::{Serialize, Deserialize};
-use chrono::{DateTime, Utc};
-use std::collections::HashMap;
 use crate::domain::entities::calendar::Calendar;
 use crate::domain::entities::calendar_event::CalendarEvent;
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use std::collections::HashMap;
 
 /// DTO for calendar data transfer
 #[derive(Debug, Serialize, Deserialize, Clone)]
@@ -178,4 +178,4 @@ pub struct EventQueryDto {
 pub struct PaginationDto {
     pub limit: Option<i64>,
     pub offset: Option<i64>,
-}
+}