Packaged desktop sidecar crashes at first DB read: jlink image omits java.sql

## Summary

The packaged desktop sidecar produced by the README's documented package path (`./gradlew packageDistributionForCurrentOS`, or `createDistributable`) crashes on its first database read with `ClassNotFoundException: java.sql.Driver`. `./gradlew run` is unaffected because it runs on the full JDK.

## Environment

- macOS 15 (arm64), Temurin JDK 21.0.12
- repo at `ccb94ae25c2b286d62e7371fd4c0f7ce60e33efa`

## Reproduce

```bash
cd desktop-sidecar
./gradlew createDistributable
./build/compose/binaries/main/app/AgentTaskQueueSidecar.app/Contents/MacOS/AgentTaskQueueSidecar --data-dir /tmp/atq-repro
```

```
Exception in thread "AWT-EventQueue-0" java.lang.NoClassDefFoundError: java/sql/Driver
at com.block.agenttaskqueue.sidecar.TaskQueueDatabase.(TaskQueueDatabase.kt:10)
...
Caused by: java.lang.ClassNotFoundException: java.sql.Driver
```

## Cause

`desktop-sidecar/build.gradle.kts`'s `nativeDistributions` block declares no `modules(...)`, so the jlink runtime image omits `java.sql` even though the project depends on `org.xerial:sqlite-jdbc` (3.53.0.0), which needs it at class-load time.

## Fix

One line in the `nativeDistributions` block:

```kotlin
modules("java.sql")
```

Happy to send the one-line PR if that's easier.