feat(ui): add vertical logo lockup splash screen on app load

Introduce a full-screen brand splash shown while the project store is
loading (status !== ready). Uses a new vertical logo lockup (P tile /
PubScript wordmark / S tile) matching the existing typewriter-tile
design, centered on the active theme background with a subtle
fade/appear animation and a graceful fade-out once the app is ready.

- apps/web/public/logo-lockup.svg: vertical lockup variant of the mark
- SplashScreen.tsx: overlay driven by the store's load status
- splash.css: full-screen overlay + keyframe animations
- wire into App.tsx and import splash.css in main.tsx

apps/web/src/components/index.ts

@@ -5,3 +5,4 @@ export type { TopbarProps } from "./Topbar.js";
 export { CommandPalette } from "./CommandPalette.js";
 export type { CommandPaletteProps } from "./CommandPalette.js";
 export { Settings } from "./Settings.js";
+export { default as SplashScreen } from "./SplashScreen.js";