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.

Open desktop-sidecar/build.gradle.kts and inspect the nativeDistributions block, then reproduce with ./gradlew createDistributable and the packaged AgentTaskQueueSidecar command from the issue. Done means the packaged sidecar completes its first database read without the java.sql.Driver ClassNotFoundException.

Written by the indexing model from the issue text.