Add org switcher with create, switch, and delete

The sidebar org button was inert: clicking it did nothing. Add a real
dropdown menu listing every organization, a "New organization" entry
that re-enters onboarding without resetting the database, and a per-org
delete affordance with inline confirmation. Active org is now persisted
in a single-row app_state table so the snapshot keeps a stable
selection across restarts and the renderer drives switching via two new
IPC channels (setActiveOrganization, deleteOrganization).

- migration 006 adds app_state(id=1, active_org_id, updated_at)
- snapshot resolves active org from app_state with the first-org fallback
- OrganizationService gains setActive + delete + bootstrap upsert
- new OrgSwitcher renderer component keeps Shell.tsx lean

AgentCompany-New/src/main/app/ipc-handlers.ts

@@ -67,6 +67,8 @@ export function registerIpcHandlers(deps: IpcDeps): void {
   });
 
   ipcMain.handle(IPC_CHANNELS.createOrganization, (_event, input) => mutate(() => organization.createOrganization(input)));
+  ipcMain.handle(IPC_CHANNELS.setActiveOrganization, (_event, input) => mutate(() => organization.setActiveOrganization(input.orgId)));
+  ipcMain.handle(IPC_CHANNELS.deleteOrganization, (_event, input) => mutate(() => organization.deleteOrganization(input.orgId)));
   ipcMain.handle(IPC_CHANNELS.createAgent, (_event, input) => mutate(() => organization.createAgent(input)));
   ipcMain.handle(IPC_CHANNELS.createTask, (_event, input) => mutate(() => organization.createTask(input)));
   ipcMain.handle(IPC_CHANNELS.updateTaskStatus, (_event, input) => mutate(() => organization.updateTaskStatus(input.orgId, input.taskId, input.status)));