feat(ui): storybook 10 over the real pages + screenshot harness

Preview imports the mock transport statically and wraps every story in
a fresh RegistryProvider seeded with mock mode + the story's scenario
parameter (dark default, light via toolbar). One story file per page
(Default + FirstRun/Syncing/Errors where meaningful) plus the whole
shell. tools/screenshots.mjs mirrors the console's harness: headless
Chromium over storybook-static, every Pages/* + Shell/* story.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ui/.storybook/main.ts

@@ -0,0 +1,12 @@
+import type { StorybookConfig } from "@storybook/react-vite";
+
+const config: StorybookConfig = {
+	stories: ["../src/**/*.stories.tsx"],
+	addons: [],
+	framework: {
+		name: "@storybook/react-vite",
+		options: {},
+	},
+};
+
+export default config;