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.

tests/unit/contracts.test.ts

@@ -11,7 +11,6 @@ describe("shared contracts", () => {
   it("fills connector defaults for optional fields", () => {
     const parsed = connectorInputSchema.parse({
       id: "openai-codex",
-      command: "codex",
     });
 
     expect(parsed.model).toBeUndefined();