[Bug]: Inconsistent REST Path Validation Between `init` and `configure`

## Expected:
Both should behave the same, either reject or normalize consistently.

```
# This silently succeeds (prepends /):
dab init --database-type mssql --connection-string "test" --rest.path "noslash" --config test.json

# This correctly fails:
dab configure --runtime.graphql.path "noslash"
# fail: Path must start with a '/'
```