Add player position tracking relay + rendering (Phase 7b)

Relays the mod's throttled player_positions roster over a new
/ws/players/:serverId gateway (Redis pub/sub + snapshot key so a
tab connecting between mod flushes isn't empty), gated per-server
by a new playerPositionsVisible admin toggle independent of the
mod's own tracking config. Frontend renders the roster as map
markers with a show/hide toggle and online count. Covered by unit
tests (players.test.ts, ws-gateway.test.ts, admin.test.ts) and a
new e2e spec that plays the real mod WS protocol from inside a
browser context.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015tKdPZt78zbPUZMXWzKEKt

frontend/src/views/admin.pug

@@ -37,7 +37,7 @@ html(lang="en")
                     input.flex-1.bg-neutral-900.text-sm.px-2.py-1.rounded.border.border-neutral-700(
                       type="text" x-model="server.name" data-testid="admin-server-name")
                     span.text-xs.text-neutral-500.font-mono.truncate(style="max-width: 14rem;" x-text="server.token" data-testid="admin-server-token")
-                  div.grid.grid-cols-3.gap-2
+                  div.grid.grid-cols-4.gap-2
                     select.bg-neutral-900.text-xs.px-2.py-1.rounded.border.border-neutral-700(
                       x-model="server.authMode" data-testid="admin-server-authmode")
                       option(value="online") online
@@ -50,6 +50,9 @@ html(lang="en")
                     label.flex.items-center.gap-1.text-xs.text-neutral-300
                       input(type="checkbox" x-model="server.anonymousChatAllowed" data-testid="admin-server-anonchat")
                       | anonymous chat
+                    label.flex.items-center.gap-1.text-xs.text-neutral-300
+                      input(type="checkbox" x-model="server.playerPositionsVisible" data-testid="admin-server-playerpositions")
+                      | player positions
                   div.flex.gap-2
                     button.px-2.py-1.bg-emerald-700.rounded.text-xs(x-on:click="saveServer(server)" data-testid="admin-server-save") Save
                     button.px-2.py-1.bg-red-800.rounded.text-xs(x-on:click="removeServer(server)" data-testid="admin-server-delete") Delete

frontend/src/views/index.pug

@@ -51,6 +51,14 @@ html(lang="en")
                   button.px-2.py-1.bg-neutral-700.rounded.text-xs(x-on:click="cancelMarkerForm" data-testid="marker-cancel") Cancel
                 p.text-xs.text-amber-400(x-show="markerStatus" x-text="markerStatus")
         aside.w-80.flex.flex-col.border-l.border-neutral-700.bg-neutral-800(x-show="server")
+          div.border-b.border-neutral-700.p-2.flex.items-center.justify-between
+            h2.text-sm.font-semibold Players
+            div.flex.items-center.gap-2
+              span.text-xs.text-neutral-400(x-text="onlinePlayers.length + ' online'" data-testid="players-online-count")
+              label.flex.items-center.gap-1.text-xs.text-neutral-300
+                input(type="checkbox" x-model="showPlayers" x-on:change="onShowPlayersChange" data-testid="players-toggle")
+                | show
+
           div.border-b.border-neutral-700.p-2.space-y-2
             div.flex.items-center.justify-between
               h2.text-sm.font-semibold Region export