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/integration/cross-subsystem.spec.ts

@@ -59,7 +59,6 @@ function scaffold(db: AppDatabase, budgetAmountCents = 500): ScaffoldResult {
 
   db.saveConnector({
     id: connectorId,
-    command: "gemini",
     model: "gemini-2.5-pro",
     envBindingText: "",
     notes: "Non-exempt connector for session rotation tests",

tests/integration/database.spec.ts

@@ -104,7 +104,6 @@ describe("AppDatabase", () => {
 
     db.saveConnector({
       id: "openai-codex",
-      command: "codex",
       model: null,
       envBindingText: "OPENAI_API_KEY=vault-openai",
       notes: "Connector note",

tests/integration/process-recovery.spec.ts

@@ -56,7 +56,6 @@ function scaffold(db: AppDatabase): ScaffoldResult {
   // Connector
   db.saveConnector({
     id: connectorId,
-    command: "gemini",
     model: "gemini-2.5-pro",
     envBindingText: "",
     notes: "Non-exempt connector for session rotation tests",