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.

index.html

@@ -3,15 +3,11 @@
 <head>
     <meta charset="UTF-8" />
     <link rel="icon" type="image/png" href="./favicon.png" />
-    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-    <link rel="stylesheet" href="./style.css">
-    <title>Sokoban — 100 Microban Puzzles</title>
+    <meta name="viewport" content="width=device-width, initial-scale=1.0, viewport-fit=cover" />
+    <title>Sokoban — 155 Puzzles</title>
 </head>
-
 <body>
-    <div id="app">
-        <div id="game-container"></div>
-    </div>
-    <script type="module" src="src/main.js"></script>
+    <div id="app"></div>
+    <script type="module" src="/src/main.js"></script>
 </body>
 </html>