v0.1.0

• Converted to a pure VS Code extension: removed the Positron language runtime,
  connection drivers, and the ggsql-jupyter kernel integration.
• Queries now run through the ggsql CLI (ggsql exec); the run button, code
  lenses, and cell keybindings all execute via the CLI.
• Generated charts are rendered with Vega-Lite in a "ggsql Results" webview
  panel beside the editor.
• New settings: ggsql.reader (data source connection string passed via
  --reader, default duckdb://memory) and ggsql.executablePath (path to
  the ggsql binary, defaults to ggsql on PATH). The ggsql.kernelPath
  setting was removed.