ui: unified rounded navbar everywhere, vertical home actions, no bot disconnect spam

- NavRail: one rounded "pill" tab bar on every screen (matches home). ScreenShell
  lays out as a portrait column and floats the nav with margins + safe-area;
  dropped the landscape side-rail variant.
- Home: the three mode cards now stack vertically as full-width rows (portrait
  friendly) instead of a 3-up landscape row.
- Disconnect: removed the simulated random opponent "disconnect" in local games
  (DISCONNECT_CHANCE) and the in-game DisconnectBanner — bots/filled seats just
  auto-play their turn; no message, no pause. (Live reconnect grace still tracked
  internally but no longer shows a banner.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/lib/game-store.ts

@@ -32,10 +32,8 @@ export const TIMING = {
 /** Base turn time (starter league / vs-AI). Higher leagues use less — see
  *  `turnMsForStake`. Kept for reference; scheduling derives the real value. */
 export const TURN_MS = 15000;
-/** Grace period to wait for a disconnected player to return. */
+/** Grace period to wait for a disconnected player to return (live games). */
 export const RECONNECT_MS = 15000;
-/** Per-turn chance an online opponent briefly drops (mock). */
-const DISCONNECT_CHANCE = 0.07;
 
 export type GameMode = "ai" | "online";
 
@@ -267,27 +265,10 @@ export const useGameStore = create<GameStore>((set, get) => {
             scheduleAuto();
           }, turnMs);
         } else {
-          const st = get();
-          if (
-            st.mode === "online" &&
-            st.disconnectedSeat == null &&
-            Math.random() < DISCONNECT_CHANCE
-          ) {
-            // simulate this opponent dropping; wait for them, then they return
-            set({
-              turnDeadline: null,
-              disconnectedSeat: seat,
-              reconnectDeadline: Date.now() + RECONNECT_MS,
-            });
-            const back = Math.floor(RECONNECT_MS * (0.4 + Math.random() * 0.45));
-            pending = setTimeout(() => {
-              set({ disconnectedSeat: null, reconnectDeadline: null });
-              playSeatAI(seat);
-            }, back);
-          } else {
-            set({ turnDeadline: null });
-            pending = setTimeout(() => playSeatAI(seat), fast(TIMING.aiPlay));
-          }
+          // Opponents (bots / filled seats) simply auto-play their turn — no
+          // simulated disconnects, no pause, no banner.
+          set({ turnDeadline: null });
+          pending = setTimeout(() => playSeatAI(seat), fast(TIMING.aiPlay));
         }
         break;
       }