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/edge-case-session.test.ts

@@ -30,7 +30,6 @@ function scaffold(db: AppDatabase, connectorId: ConnectorId = "gemini-cli") {
   // Always save gemini-cli (needed for most tests)
   db.saveConnector({
     id: "gemini-cli",
-    command: "gemini",
     model: "gemini-pro",
     envBindingText: "",
     notes: "Test connector - no native context management",