Add: tauri frontend as bevy alternative

docs/TAURI_FRONTEND_DESIGN.md

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+# Tauri 2.0 Frontend Design (Bevy Alternative)
+
+Date: 2026-02-12
+
+## Goal
+
+Add a Tauri 2.0 frontend path as an alternative to Bevy while keeping the existing Bevy
+implementation and API behavior.
+
+## New Components
+
+- `crates/sprimo-runtime-core`
+  - shared runtime bootstrap for config/snapshot/API/channel setup
+  - shared command-to-snapshot/config application
+- `crates/sprimo-tauri`
+  - Tauri 2.0 desktop shell
+  - command consumer loop bound to runtime core
+  - invoke command `current_state` for UI state
+- `frontend/tauri-ui`
+  - React + Vite UI shell for status/control surface
+
+## Selected Crates
+
+Rust:
+
+- `tauri`
+- `tauri-build`
+- `tauri-plugin-log`
+- `tauri-plugin-global-shortcut`
+- existing internal crates:
+  - `sprimo-runtime-core`
+  - `sprimo-platform`
+  - `sprimo-protocol`
+
+Frontend:
+
+- `react`
+- `react-dom`
+- `vite`
+- `typescript`
+- `@tauri-apps/api`
+
+## Current State
+
+- Tauri binary crate is scaffolded and starts runtime core + API server.
+- Runtime core receives API commands and updates shared snapshot/config state.
+- Tauri backend exposes:
+  - `current_state` command (structured snapshot DTO)
+  - `load_active_sprite_pack` command (manifest + atlas as base64 data URL)
+  - `runtime:snapshot` event after command application.
+- React/Vite frontend now renders sprite atlas frames with PixiJS and updates animation/scale
+  from runtime snapshot events.
+- Bevy frontend remains intact.
+- Runtime QA workflow is defined in `docs/TAURI_RUNTIME_TESTING.md`.
+
+## Remaining Work
+
+1. Move Bevy runtime flow to consume `sprimo-runtime-core` as primary state authority.
+2. Add tray/menu parity and window behavior parity with Bevy path.
+3. Extend packaging scripts to include `sprimo-tauri` artifact path.
+4. Add frontend parity acceptance tests (Bevy vs Tauri state transitions).