Upgrade to Kotlin 2.4.10 / AGP 9.1.1 and add on-screen keyboard UX

[joreilly]

Summary

Two related pieces of work:

Dependency / toolchain upgrade (versions queried from live registries, not guessed)

• Kotlin 2.2.0 → 2.4.10, KSP → 2.3.10, coroutines → 1.11.0
• AGP 8.12.0 → 9.1.1; Gradle wrapper 9.0.0 → 9.6.1 (AGP 9.1.1 needs ≥9.3.1)
• Compose Multiplatform 1.8.2 → 1.11.1, activity-compose 1.13.0, compose-bom 2026.06.01, lifecycle 2.11.0, okio 3.17.0, kmp-nativecoroutines 1.0.5
• AGP 9 migration: shared moves to com.android.kotlin.multiplatform.library; androidApp drops kotlin("android") (built-in Kotlin). Config moved into kotlin { android { } }.
• compileSdk/targetSdk 36 → 37 — forced by lifecycle 2.11.0.
• iOS SwiftPM pin for KMP-NativeCoroutines aligned to 1.0.5 to match the Gradle plugin.
• CI updated: :shared:testDebugUnitTest → :shared:jvmTest (the former no longer exists under the new plugin).

On-screen keyboard UX overhaul

• Replaced the editable-TextField-per-cell boards (and their brittle FocusRequester juggling) with read-only tiles driven by a shared on-screen QWERTY keyboard.
• WordMasterService gains addLetter / removeLetter / submitGuess, word-list validation (isValidWord), a keyStatus flow that colours the keyboard by best-known letter status, and a guessError flow for feedback.
• Rejected guesses now shake the active row + show a message ("Not enough letters" / "Not in word list") instead of failing silently.
• Applied across Android (Material 3), Desktop (Material 2, also wired to the physical keyboard), and iOS (SwiftUI).

Test plan

• ./gradlew :androidApp:assembleDebug
• ./gradlew :compose-desktop:assemble
• ./gradlew :shared:jvmTest (existing logic test still green)
• ./gradlew :shared:compileKotlinIosArm64 + framework link
• Full iOS app xcodebuild for the simulator → BUILD SUCCEEDED
• Screenshot in README still shows the old UI — needs a fresh capture from a running client

Note: WordMasterServiceTest fails on iosSimulatorArm64Test due to a pre-existing relative-path bug (../words.txt doesn't resolve in the simulator sandbox); confirmed it fails identically on main before these changes, so it's out of scope here.

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