feat(frontend): restructure main menu into Solo/Private/Matchmaking

Replace the single pick-a-theme-and-start intro modal with a three-section
menu (Solo/Private/Matchmaking). Solo keeps the existing gameplay reachable
via a direct Play button; Private (Enter Code/Create Room) and Matchmaking
(Find Match) are stubbed with console.log no-ops pending tickets #17/#15/#14.

main.ts gains a small showView(name) helper that toggles .hidden across the
menu/result overlay screens, keeping it a thin composition root.

frontend/index.html

@@ -60,18 +60,38 @@
   </div>
 
   <div id="intro-modal" class="modal-overlay">
-    <div class="modal">
+    <div class="modal menu-modal">
       <h2>🕹️ THEME GUESS</h2>
-      <p>A snippet of code is hiding a classic color theme.</p>
+      <p>A snippet of code is hiding a classic color theme. Pick how you want to play.</p>
-      <ol>
+
-        <li>Click any word in the code — every token of that <em>kind</em> lights up together.</li>
+      <div class="menu-sections">
-        <li>Pick a color for that kind. Watch it paint everywhere at once.</li>
+        <section id="menu-solo" class="menu-section" aria-label="Solo">
-        <li>Repeat until all 12 kinds have a color, including the background.</li>
+          <h3>🧑‍💻 SOLO</h3>
-        <li>Hit <strong>REVEAL MATCH</strong> to see how close your palette lands to the real thing.</li>
+          <p class="menu-section-desc">Click any word to color it, then reveal how close your palette lands to the real theme.</p>
-      </ol>
+          <p class="pick-theme-label">▼ PICK A THEME ▼</p>
-      <p class="pick-theme-label">▼ PICK YOUR TARGET THEME ▼</p>
+          <div id="theme-grid" class="theme-grid"></div>
-      <div id="theme-grid" class="theme-grid"></div>
+          <div class="menu-section-actions">
-      <button id="start-btn" class="btn primary big">▶ PRESS START</button>
+            <button id="start-btn" class="btn primary">▶ PLAY</button>
+          </div>
+        </section>
+
+        <section id="menu-private" class="menu-section" aria-label="Private">
+          <h3>🔒 PRIVATE</h3>
+          <p class="menu-section-desc">Play with friends in a private room, by invite code or a fresh room.</p>
+          <div class="menu-section-actions">
+            <button id="enter-code-btn" class="btn ghost">Enter Code</button>
+            <button id="create-room-btn" class="btn ghost">Create Room</button>
+          </div>
+        </section>
+
+        <section id="menu-matchmaking" class="menu-section" aria-label="Matchmaking">
+          <h3>🌐 MATCHMAKING</h3>
+          <p class="menu-section-desc">Get paired with another player looking for a match right now.</p>
+          <div class="menu-section-actions">
+            <button id="find-match-btn" class="btn primary">Find Match</button>
+          </div>
+        </section>
+      </div>
     </div>
   </div>
 

frontend/src/main.ts

@@ -12,14 +12,17 @@ function requireEl<T extends HTMLElement>(id: string): T {
   return el as T;
 }
 
-const introModal = requireEl<HTMLElement>('intro-modal');
+const menuModal = requireEl<HTMLElement>('intro-modal');
+const resultModal = requireEl<HTMLElement>('result-modal');
 const themeGridEl = requireEl<HTMLElement>('theme-grid');
 const startBtn = requireEl<HTMLButtonElement>('start-btn');
+const enterCodeBtn = requireEl<HTMLButtonElement>('enter-code-btn');
+const createRoomBtn = requireEl<HTMLButtonElement>('create-room-btn');
+const findMatchBtn = requireEl<HTMLButtonElement>('find-match-btn');
 const helpBtn = requireEl<HTMLButtonElement>('help-btn');
 const muteBtn = requireEl<HTMLButtonElement>('mute-btn');
 const themeNameBadge = requireEl<HTMLElement>('theme-name-badge');
 const changeThemeBtn = requireEl<HTMLButtonElement>('change-theme-btn');
-const resultModal = requireEl<HTMLElement>('result-modal');
 
 const previewElements = {
   overlay: requireEl<HTMLElement>('preview-overlay'),
@@ -28,13 +31,32 @@ const previewElements = {
   canvas: requireEl<HTMLCanvasElement>('preview-canvas'),
 };
 
+/** Top-level overlay screens the composition root switches between. At most
+ * one is visible at a time; the game board underneath is always present and
+ * simply gets obscured while a screen is shown. */
+const screens = {
+  menu: menuModal,
+  result: resultModal,
+} as const;
+
+type ScreenName = keyof typeof screens;
+
+function showView(name: ScreenName | null): void {
+  for (const key of Object.keys(screens) as ScreenName[]) {
+    screens[key].classList.toggle('hidden', key !== name);
+  }
+}
+
 let game: ThemeGuessGame | null = null;
 
 const themeGrid = createThemeGrid(themeGridEl, 'gruvbox', () => sound.playOpen());
 
-function startWithSelectedTheme(): void {
+// Solo is the only flow this ticket wires end-to-end. Ticket #17 will
+// replace this direct "pick a theme, hit play" shortcut with a fuller solo
+// config flow inside #menu-solo; keep it working in the meantime.
+function playSolo(): void {
   const themeId: ThemeId = themeGrid.selected;
-  introModal.classList.add('hidden');
+  showView(null);
   runThemePreview(previewElements, themeId, () => {
     if (game) game.setTheme(themeId);
     else game = new ThemeGuessGame(themeId);
@@ -43,14 +65,21 @@ function startWithSelectedTheme(): void {
   }, () => sound.playOpen());
 }
 
-startBtn.addEventListener('click', startWithSelectedTheme);
+startBtn.addEventListener('click', playSolo);
-helpBtn.addEventListener('click', () => introModal.classList.remove('hidden'));
+
-changeThemeBtn.addEventListener('click', () => {
+// TODO(#17/#15/#14): wire real flow
-  resultModal.classList.add('hidden');
+enterCodeBtn.addEventListener('click', () => console.log('[menu] enter code clicked (not implemented yet)'));
-  introModal.classList.remove('hidden');
+// TODO(#17/#15/#14): wire real flow
-});
+createRoomBtn.addEventListener('click', () => console.log('[menu] create room clicked (not implemented yet)'));
+// TODO(#17/#15/#14): wire real flow
+findMatchBtn.addEventListener('click', () => console.log('[menu] find match clicked (not implemented yet)'));
+
+helpBtn.addEventListener('click', () => showView('menu'));
+changeThemeBtn.addEventListener('click', () => showView('menu'));
 
 muteBtn.addEventListener('click', () => {
   const muted = sound.toggleMute();
   muteBtn.textContent = muted ? '🔇' : '🔊';
 });
+
+showView('menu');

frontend/src/style.css

@@ -380,6 +380,49 @@ body {
   text-align: center;
 }
 
+/* ---------- main menu (Solo / Private / Matchmaking) ---------- */
+
+.menu-modal { max-width: 760px; }
+
+.menu-sections {
+  display: grid;
+  grid-template-columns: repeat(3, 1fr);
+  gap: 14px;
+  margin: 18px 0 4px;
+}
+
+.menu-section {
+  background: var(--panel-2);
+  border: 3px solid var(--ink);
+  box-shadow: 4px 4px 0 var(--ink);
+  padding: 14px;
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+.menu-section h3 {
+  margin: 0;
+  font-family: var(--pixel);
+  font-size: 11px;
+  text-shadow: 1px 1px 0 var(--ink);
+}
+
+#menu-solo h3 { color: var(--cyan); }
+#menu-private h3 { color: var(--pink); }
+#menu-matchmaking h3 { color: var(--green); }
+
+.menu-section-desc { margin: 0; font-size: 11px; line-height: 1.5; color: var(--fg-dim); }
+
+.menu-section-actions { display: flex; flex-direction: column; gap: 8px; margin-top: auto; }
+.menu-section-actions .btn { width: 100%; }
+
+#menu-solo .theme-grid { margin-bottom: 0; }
+
+@media (max-width: 640px) {
+  .menu-sections { grid-template-columns: 1fr; }
+}
+
 /* ---------- theme preview countdown ---------- */
 
 .preview-box {