️🛠 - Restructure codebase into monorepo layout

[maxwellmattryan]

Description

Restructure the project into a monorepo layout to support separate desktop and mobile frontends while sharing types, stores, API wrappers, utilities, and i18n.

This must happen before any mobile frontend code is written.

Scope:

• Move src/ to apps/desktop/src/
• Extract shared code to shared/:
  • types/ — all TypeScript type definitions
  • api/ — all Tauri IPC wrappers (same invoke() calls used by both platforms)
  • stores/ — shared stores: discovery, discoveryPlaylist, expandedReleases, player, tags, playlists, settings, toast
  • utils/ — format, sorting, selection, storage, artwork utilities
  • i18n/ — all locale files and i18n setup
  • services/previewPlayer.ts — HTML5 Audio singleton
• Desktop-only stores stay in apps/desktop/src/lib/stores/: devices, export, sync (USB), analysis, drag, app, crash, diagnostics, missingTracks, updater, splash, backup, pageActions
• Desktop-only components, controllers, and hooks stay in apps/desktop/
• Update Tauri configs (tauri.conf.json, tauri.dev.conf.json, etc.) to point to apps/desktop/
• Add $shared path alias in both svelte.config.js and vite.config.ts pointing to ../../shared/
• Scaffold apps/mobile/ with SvelteKit, own svelte.config.js, vite.config.ts, same $shared alias
• Update all import paths throughout the desktop frontend
• Verify desktop build works identically after restructuring

Key files:

• src/ → apps/desktop/src/
• shared/ — new directory
• apps/mobile/ — new scaffolded directory
• svelte.config.js, vite.config.ts — both apps
• src-tauri/tauri.conf.json and environment-specific configs

Open questions

• Should the root package.json use Yarn workspaces, or keep a single package.json with path aliases only?
• Should svelte.config.js and vite.config.ts live in apps/desktop/ or remain at root with the mobile equivalents added alongside?
• Should the ui store be split (shared core state vs. desktop-specific layout state) or kept entirely in desktop?

Acceptance criteria

• Desktop application builds and runs identically after restructuring (no functional changes)
• apps/desktop/src/ contains only desktop-specific code (components, controllers, hooks, desktop-only stores)
• shared/ contains types, API wrappers, shared stores, utils, i18n, and previewPlayer service
• apps/mobile/ is scaffolded with SvelteKit and can import from $shared
• All import paths are updated and resolve correctly
• src-tauri/ is unchanged in location and continues to serve both platforms
• Tauri configs correctly reference apps/desktop/ for frontend

Tasks

TBD