feat: add MotherDuck support to CLI

Add --database-path and --mother-duck-token options to the create-duckdb
command to allow users to configure MotherDuck connections via the CLI.

Changes:
- Add --database-path flag to create-duckdb command (removed -d short
  option to avoid conflict with global --debug flag)
- Add --mother-duck-token flag for MotherDuck API token
- Add additionalExtensions field to DuckDBConnectionOptions/Config
- Document MotherDuck usage in README with examples

Signed-off-by: James Swirhun <james@ms2.co>

Author: jswir

README.md

@@ -15,3 +15,39 @@ npx malloy-cli ...
 ```
 
 Documentation is available on the [Malloy documentation website](https://malloydata.github.io/documentation/malloy_cli/index).
+
+## MotherDuck Support
+
+The CLI supports [MotherDuck](https://motherduck.com/) connections. To connect to MotherDuck, use a database path that starts with `md:` or `motherduck:`.
+
+### Option 1: CLI with token flag
+
+```shell
+malloy-cli connections create-duckdb my-motherduck \
+  --database-path "md:my_database" \
+  --mother-duck-token "your_motherduck_token"
+```
+
+### Option 2: Environment variable
+
+```shell
+export MOTHERDUCK_TOKEN="your_token"
+malloy-cli connections create-duckdb my-motherduck --database-path "md:my_database"
+```
+
+### Option 3: Config file
+
+Create or edit your config file (typically `~/.config/malloy/config.json`):
+
+```json
+{
+  "connections": [{
+    "name": "motherduck",
+    "backend": "duckdb",
+    "databasePath": "md:my_database",
+    "motherDuckToken": "your_token"
+  }]
+}
+```
+
+**Token precedence:** config value > `MOTHERDUCK_TOKEN` env var > `motherduck_token` env var

src/cli.ts

@@ -231,7 +231,8 @@ export function createCLI(): Command {
     .command('create-duckdb')
     .description('add a new DuckDB database connection')
     .argument('<name>')
-    .option('-d, --database-path <database>')
+    .option('--database-path <path>', 'path to DuckDB database file or MotherDuck (e.g., md:database_name)')
+    .option('--mother-duck-token <token>', 'MotherDuck API token')
     .action(createDuckDbConnectionCommand);
 
   connections

src/connections/connection_types.ts

@@ -85,13 +85,15 @@ export interface DuckDBConnectionOptions {
   workingDirectory?: string;
   databasePath?: string;
   motherDuckToken?: string;
+  additionalExtensions?: string[];
 }
 
 export interface DuckDBConnectionConfig extends BaseConnectionConfig {
   backend: ConnectionBackend.DuckDB;
   workingDirectory?: string;
   databasePath?: string;
   motherDuckToken?: string;
+  additionalExtensions?: string[];
 }
 
 export interface SnowflakeConnectionOptions {