Add Compose UI smoke tests for article flow

[leesunghyun]

Summary

Adds first Compose UI smoke tests for the critical article flow and adds stable testTags for deterministic UI testing.

What changed

• Added androidx.compose.ui:ui-test-junit4 to androidTest dependencies.
• Added testTag markers to list/detail screens for deterministic node selection.
• Added ArticleUiSmokeTest with scenarios:
  • Edit first article title/body and save, then verify updated title appears in list.
  • Delete first article and verify its row is removed.

Scope

• Test support + small UI instrumentation for v0.2 readiness.

Notes

This is a smoke-level coverage baseline for key migration flow:
List → Detail → Edit → Save → List and delete interaction.

Current CI in this repo only runs:

• ./gradlew test
• ./gradlew assembleDebug

So instrumented UI tests are not executed in the default pipeline yet.