feat!: rewrite on Svelte 5, drop Phaser

Replace Phaser 3 with Svelte 5 as the rendering and UI layer. The
framework-agnostic core (level parser, board model, progress store,
microban level data) moves from src/game/core → src/lib/core with zero
code changes. Scenes and the hand-rolled button factory are gone; in
their place:

- src/App.svelte            root router (menu / levels / game)
- src/views/MenuView        title + play + progress + hints
- src/views/LevelSelectView paginated 5x4 grid with native <button>s
- src/views/GameView        owns BoardModel, handles input, HUD, win
- src/views/Board           purely presentational DOM renderer
- src/views/AppButton       shared themed wrapper for native <button>
- src/app.css               Nord palette ported to CSS variables

GameView uses a non-reactive BoardModel ref and syncs plain snapshot
fields (player, boxes, moves, won) into $state after every mutation —
Board consumes only plain props, so Svelte reactivity stays predictable
and the core class stays framework-agnostic. GameView is keyed on
levelIndex in App, so changing level remounts with fresh state.

Native <button> everywhere kills the click-hitbox class of bugs.
Animations are now CSS transform transitions (110ms) instead of tweens.

Bundle shrinks from ~1.5 MB Phaser to ~65 kB JS / 23 kB gzipped — about
60x smaller. Removed: phaser, terser, src/game, log.js (analytics
ping), phasermsg vite plugin, manual Phaser chunks, terser config,
public/style.css. Scripts simplified to dev/build.

Docs updated: codebase summary, architecture, code standards,
changelog, roadmap, README.

package.json

@@ -15,16 +15,12 @@
   },
   "homepage": "https://tiennm99.github.io/sokoban/",
   "scripts": {
-      "dev": "node log.js dev & vite --config vite/config.dev.mjs",
-      "build": "node log.js build & vite build --config vite/config.prod.mjs",
-      "dev-nolog": "vite --config vite/config.dev.mjs",
-      "build-nolog": "vite build --config vite/config.prod.mjs"
+      "dev": "vite --config vite/config.dev.mjs",
+      "build": "vite build --config vite/config.prod.mjs"
   },
   "devDependencies": {
-    "terser": "^5.39.0",
+    "@sveltejs/vite-plugin-svelte": "^5.0.3",
+    "svelte": "^5.19.0",
     "vite": "^6.3.6"
-  },
-  "dependencies": {
-    "phaser": "^3.88.2"
   }
 }