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/shared/ipc.ts

@@ -1,6 +1,8 @@
 export const IPC_CHANNELS = {
   loadSnapshot: "agentcompany:load-snapshot",
   bootstrapOnboarding: "agentcompany:bootstrap-onboarding",
+  setActiveOrganization: "agentcompany:set-active-organization",
+  deleteOrganization: "agentcompany:delete-organization",
   createOrganization: "agentcompany:create-organization",
   createAgent: "agentcompany:create-agent",
   createTask: "agentcompany:create-task",