Execute clean tenant context swap via TenantContextService

The MultiOrgContextSwitcherCubit should hold previousActiveOrgId in its state so rollback on error requires no additional API call. Use a BlocListener in the MultiOrgContextSwitcher widget to react to success/error states: on success, call Navigator.of(context).pop() to close the sheet, then use a callback or event bus to update ActiveTenantCubit at the app level, then navigate via GoRouter. Avoid calling GoRouter inside the bottom sheet's context — instead, pass a VoidCallback onSwitchSuccess to the sheet widget, or use a stream/event bus listened to at the root Navigator level. For cache invalidation, trigger a global ClearTenantDataEvent on the relevant repository Cubits after a successful switch — define a common interface or use an event bus (e.g., a stream exposed by TenantContextService).

ActiveTenantCubit should be provided at the MaterialApp level so the AppBar can rebuild reactively. Apply design tokens for branding updates (org accent color) via the ActiveTenantCubit state, not by directly manipulating ThemeData at runtime.

Write Cubit unit tests: (1) emits [switching, switchSuccess] on successful TenantContextService call, (2) emits [switching, switchError] with previousActiveOrgId preserved on failure, (3) ActiveTenantCubit is notified on success. Write widget tests: (4) loading overlay blocks interaction during switch, (5) sheet is dismissed on success, (6) ActiveTenantIndicator in app bar reflects new org after success, (7) failure shows inline error and restores previous active org highlight in list, (8) retry on failure re-dispatches ConfirmOrgSwitch. Integration test: simulate a full switch flow from tap → dialog confirm → loading → success → home screen navigation. Use flutter_test, bloc_test, and mock TenantContextService.