docs: document download peer count chip

Update the launcher design reference so active downloads show how many LAN
peers are currently seeding the transfer. The reference now places the peer
chip between speed and ETA, describes the singular/plural copy, and records
how the ETA and peer count collapse in narrow modal layouts.

Test Plan:
- git diff --cached --check

design/design_reference/data.jsx

@@ -18,7 +18,7 @@ const GAMES = [
   {
     id: 'avp', title: 'Aliens vs. Predator', size: 35.0, version: '2019.10.01',
     desc: "Three campaigns, three nightmares. Be the alien stalking the dark, the predator hunting both, or the marine just trying to make it home with a working flashlight.",
-    state: 'downloading', progress: 0.32, speed: 49.4, players: '2–16', tags: ['FPS', 'Horror', 'Multiplayer'],
+    state: 'downloading', progress: 0.32, speed: 49.4, peers: 5, players: '2–16', tags: ['FPS', 'Horror', 'Multiplayer'],
     cover: { c1: '#064e3b', c2: '#020617', accent: '#34d399', mood: 'dark' },
   },
   {
@@ -120,7 +120,7 @@ const GAMES = [
   {
     id: 'quake3', title: 'Quake III Arena', size: 0.5, version: '2010.08.15',
     desc: "Arena FPS in its most distilled form. Rocket jumps, rail-gun duels, and a netcode that's still the benchmark.",
-    state: 'downloading', progress: 0.71, speed: 12.8, players: '2–16', tags: ['FPS', 'Arena', 'LAN'],
+    state: 'downloading', progress: 0.71, speed: 12.8, peers: 3, players: '2–16', tags: ['FPS', 'Arena', 'LAN'],
     cover: { c1: '#7f1d1d', c2: '#0a0a0a', accent: '#fbbf24', mood: 'dark' },
   },
   {