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/database.test.ts

@@ -96,7 +96,6 @@ describe("AppDatabase", () => {
     });
     db.saveConnector({
       id: "openai-codex",
-      command: "codex",
       model: "gpt-5",
       envBindingText: "OPENAI_API_KEY=vault-openai",
       notes: "Primary coding connector",
@@ -197,7 +196,6 @@ describe("AppDatabase", () => {
     });
     db.saveConnector({
       id: "openai-codex",
-      command: "codex",
       model: "gpt-5",
       envBindingText: "",
       notes: "Test connector",