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.

public/style.css

@@ -1,37 +0,0 @@
-:root {
-    --bg: #1c2230;
-    --accent: #88C0D0;
-}
-
-* {
-    box-sizing: border-box;
-}
-
-html, body {
-    margin: 0;
-    padding: 0;
-    height: 100%;
-    color: #ECEFF4;
-    background: radial-gradient(circle at 30% 20%, #2E3440 0%, #1c2230 60%, #0f131c 100%);
-    font-family: 'Trebuchet MS', Arial, sans-serif;
-    -webkit-font-smoothing: antialiased;
-}
-
-#app {
-    width: 100%;
-    height: 100vh;
-    display: flex;
-    justify-content: center;
-    align-items: center;
-    overflow: hidden;
-}
-
-#game-container {
-    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.6);
-    border-radius: 12px;
-    overflow: hidden;
-}
-
-canvas {
-    display: block;
-}