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/orchestration/turn-context.ts

@@ -360,7 +360,6 @@ export function buildRunPayload(params: RunDispatchParams, deps: TurnContextDeps
     workspaceId: workspaceMode === "exclusive" ? (workspace?.id ?? null) : null,
     workspacePath: workspace?.localPath ?? null,
     workspaceMode,
-    command: connector.command,
     model: modelSelection.effectiveModel,
     thinkingEffort,
     env,