[codex] refresh chat ui and toolchain

[lennney]

What changed

• Refreshed the main chat screen into a more polished local-note style layout with a dark gradient background, denser message bubbles, a system hint chip, and an updated input bar.
• Updated the theme and typography tokens to match the new visual direction.
• Upgraded the Android/Kotlin/Compose build setup to the newer plugin and Gradle versions required by the UI changes.
• Added local tools/ helper scripts and ignored the local cache directories they generate.

File record

• .gitignore: ignores .android-local/, .gradle-local/, .x-cmd-home/, and tools/.x-cmd-cache/.
• app/build.gradle.kts: enables the Compose compiler plugin and removes the old compiler extension config.
• app/src/main/java/com/example/wordsback/MainActivity.kt: replaces the old chat composition with the new screen layout and message model.
• app/src/main/java/com/example/wordsback/ui/theme/Theme.kt: refreshes the dark color scheme.
• app/src/main/java/com/example/wordsback/ui/theme/Type.kt: defines a custom type scale for the new UI.
• build.gradle.kts: upgrades AGP, Kotlin, and the Compose plugin.
• gradle.properties: adds the AGP compatibility flags needed by the upgrade.
• gradle/wrapper/gradle-wrapper.properties: upgrades the Gradle wrapper.
• tools/xcmd-local-install.ps1, tools/xcmd-local.cmd, tools/xcmd-local.ps1: adds local x-cmd helper scripts.

Validation

• git diff --check
• ./gradlew.bat assembleDebug was attempted locally, but the build is still blocked by Android SDK license acceptance in this environment.