[State Sync Redesign 3.12] Update Storybook state mocks

`.storybook/preview.js` creates a global Redux store from `.storybook/test-data.js` which uses the full flat `metamask: { ... }` shape. 60+ individual story files also mock or mutate `state.metamask` directly.

## Steps

1. Update `.storybook/test-data.js` to provide state via `ControllerStateManager` (or extend the flat-to-keyed auto-mapping from `renderWithControllerState` to Storybook)
2. Update `.storybook/preview.js` `metamaskDecorator` to wrap stories with the `ControllerStateManager` provider alongside Redux
3. Audit 60+ story files that reference `state.metamask` — update per-story mock shapes
4. **Optimization:** If the auto-mapping shim from Issue 3.2 (`renderWithControllerState`) works for test utilities, adapt it for Storybook to defer individual story rewrites

## Files

- `.storybook/test-data.js`
- `.storybook/preview.js`
- `ui/**/*.stories.*`

## Risk

Low — Storybook is a development tool, not production code. Broken stories don't block releases.

## Dependencies

Issue 3.2 (test utility with auto-mapping), can proceed in parallel with component migration (Issue 3.7)

## Context

Part of [State Sync Redesign — Epic 3: UI-controller subscriptions].

Start with .storybook/test-data.js and .storybook/preview.js, then read Issue 3.2 for the proposed auto-mapping approach. Audit the state.metamask references under ui/**/*.stories.* and verify that Storybook stories use the ControllerStateManager provider and updated mock shapes without breaking story rendering.

Written by the indexing model from the issue text.