refactor(connectors): drop dead CLI command field after pi-mono migration

The CLI-adapter era `connector.command` field became vestigial once every
provider dispatch went through pi-ai. The schema still required a non-empty
command, so onboarding saveConnector silently rejected every Pi Mono row
(which carries an empty default). Remove the field from the payload chain
(renderer → IPC schema → DB CRUD → run dispatch → worker job), narrow
RunJob.taskId to match EnqueueRunPayload, and drop the dead helper plus
its test. Schema column stays NOT NULL for DB compatibility; seedConnectors
writes a literal empty string so no migration is needed.

src/main/database-base.ts

@@ -289,7 +289,7 @@ export class AppDatabaseBase {
 
   // ─── Connectors ────────────────────────────────────────────────────────────
 
-  saveConnector(input: { id: ConnectorId; command: string; model: string | null; envBindingText: string; notes: string }) { this.connectorsCrud.saveConnector(input); }
+  saveConnector(input: { id: ConnectorId; model: string | null; envBindingText: string; notes: string }) { this.connectorsCrud.saveConnector(input); }
   updateConnectorHealth(input: { id: ConnectorId; status: string; authState: string; version: string | null; lastError: string | null }) { this.connectorsCrud.updateConnectorHealth(input); }
   getConnector(id: ConnectorId) { return this.connectorsCrud.getConnector(id); }
   findConnector(id: ConnectorId) { return this.connectorsCrud.findConnector(id); }