[Feature/#5] Migrate to Compose Multiplatform

[DongChyeon]

🎯 Related Issue

• Closes Migrate To Compose Multi Platform #5

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📝 Description

What does this PR do?

Migrates the existing project to Kotlin Multiplatform (KMP* with full Compose Multiplatform support for Android, Desktop, and iOS.
This refactor restructures the entire project architecture while preserving the main branch’s history for traceability.

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✅ Changes

• Reinitialize project structure using Compose Multiplatform templates
• Configure Android, iOS and Desktop (JVM) targets under unified KMP Gradle configuration
• Add Coil 3 + Ktor configuration for platform-dependent networking
• Update .gitignore to support KMP-specific cache and build outputs
• Preserve previous main branch history while replacing all file contents with the new project setup

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🔍 Screenshots / Test Results (if applicable)

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👤 Reviewer Checklist

• Verify Gradle sync and build succeed on Android Studio
• Check that Android and Desktop targets run successfully

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✨ Summary

This PR completes the Compose Multiplatform migration while keeping all previous project history intact.
The new setup enables shared UI and logic across Android, iOS, and Desktop platforms with clean modular design.

[Copilot]

Pull Request Overview

This PR migrates the existing Android calendar library project to Kotlin Multiplatform (KMP) with Compose Multiplatform support, enabling the same codebase to run on Android, iOS, and Desktop platforms. The migration completely restructures the project while preserving Git history for traceability.

• Replaces Android-specific project structure with KMP architecture using composeApp and multiplatform calendar module
• Migrates from Android-only dependencies to multiplatform equivalents (Coil 3, Ktor, kotlinx-datetime)
• Updates build configuration to support Android, iOS, and Desktop targets with unified Gradle setup

Reviewed Changes

Copilot reviewed 55 out of 93 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
settings.gradle.kts	Updates project structure to include composeApp module and removes old app module
gradle/libs.versions.toml	Migrates to multiplatform dependency versions and adds KMP-specific plugins
composeApp/	New multiplatform app module with platform-specific entry points for Android, iOS, and Desktop
calendar/build.gradle.kts	Converts calendar module from Android library to KMP library with multiplatform targets
iosApp/	Adds complete iOS application structure with Xcode project and Swift integration

Files not reviewed (1)

• iosApp/iosApp.xcodeproj/project.xcworkspace/contents.xcworkspacedata: Language not supported

Comments suppressed due to low confidence (1)

calendar/src/commonMain/kotlin/com/dongchyeon/calendar/ui/component/DayBackgroundImage.kt:1

• Debug print statements should be removed from production code. These println statements appear to be temporary debugging code and should either be removed or replaced with proper logging if needed.

package com.dongchyeon.calendar.ui.component

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