feat: show compose progress in home timeline

[Tlaster]

Summary

• persist compose target state, step progress, and remote post keys in the draft outbox
• show sending, sent, and failed posts as full-width cards in native home timelines
• aggregate cross-post targets while keeping failed targets editable, retryable, and removable
• return a unified ComposeResult(remotePostKey?) from supported platforms for replacement and deduplication
• remove successful targets after the real remote post appears or after one successful timeline refresh

Scope

• Android, Desktop, iOS, and macOS
• home timelines only
• Web remains unchanged
• network-result uncertainty and duplicate-send behavior remain unchanged

Testing

• ./gradlew :shared:jvmTest --tests 'dev.dimension.flare.ui.presenter.compose.SendDraftUseCaseTest' --tests 'dev.dimension.flare.data.repository.DraftRepositoryTest' --tests 'dev.dimension.flare.data.database.app.AppDatabaseMigration11To12Test'
• ./gradlew :feature:agent:jvmTest --tests 'dev.dimension.flare.feature.agent.common.AgentToolsTest'
• ./gradlew :app:compileDebugKotlin :desktopApp:compileKotlin
• ktlint checks for changed shared, Compose UI, agent, and social source sets
• iOS simulator build
• macOS build

Close #2096