dev --logs on harness-only project exits 0 instead of failing

`agentcore dev --logs` on a harness-only project prints guidance text and exits 0. It should exit 1 with a
validation error since no dev server can be started, harness projects don't support local dev.

**Reproduction**:

```
agentcore create --name MyHarness
cd MyHarness
agentcore dev --logs --skip-deploy
# Prints "Harness dev runs against the deployed service..." and exits 0
```

**Expected**: Exit code 1 with a clear error (e.g. "Harness projects do not support local dev. Use agentcore
invoke --harness instead.")

**Actual**: Exit code 0 with informational text.