feat: add React frontend with search and mod pages

Add apps/web (Vite + React Router + Tailwind v4 + Zustand) with a search page and a mod page that analyzes saves via @tts/extract. Document the frontend in the README and docs.

docs/decisions.md

@@ -95,4 +95,20 @@ available in Node.
 `<img>` / `<object>` elements.
 
 **Alternatives considered:** Raw `ArrayBuffer`. Rejected — less convenient for
-frontend rendering.
+frontend rendering.
+
+## D9 — Frontend stack: React + React Router + Tailwind v4 + Zustand
+
+**Decision:** The frontend (`apps/web`) uses React with React Router for
+routing, Tailwind CSS v4 for styling, and Zustand for state, built with Vite.
+
+**Context:** The frontend consumes the proxy API for search/fetch and
+`packages/extract` directly for analysis. React is the de-facto standard for
+this kind of tool; React Router provides declarative routes (`/` and
+`/mod/:id`); Tailwind v4 is the current major version and integrates via
+`@tailwindcss/vite`; Zustand is a minimal, unopinionated store that fits the
+small amount of client state (search + mod).
+
+**Alternatives considered:** Next.js (heavier than needed for a client-only
+tool); Redux Toolkit (more boilerplate than warranted); CSS Modules (no
+utility styling).