FX1: README capture recipes — add render-readiness wait before screenshot

Screenshotting immediately after 'simctl launch' grabs the blank white
launch screen, not the rendered board. Add an explicit 'sleep 2' between
launch and screenshot in the main capture recipe, and state a once-stated
render-readiness rule (near the first recipe) that every pinned-launch
section below references, so a clean-checkout reader reproduces the board.
Docs-only: no .sx/asset/golden change.

README.md

@@ -49,12 +49,23 @@ udid=$(xcrun simctl list devices available | grep -Eo '[0-9A-Fa-f-]{36}' | head
 xcrun simctl boot "$udid" || true
 open -a Simulator
 
-# Install, launch (bundle id co.swipelab.m3te), and screenshot:
+# Install, launch (bundle id co.swipelab.m3te), wait for the board to render, then
+# screenshot. The wait is REQUIRED: screenshotting immediately after `launch` grabs
+# the blank white launch screen, before the scene has drawn. ~2 s is ample; poll the
+# screenshot if you want it tighter.
 xcrun simctl install booted sx-out/ios/M3te.app
 xcrun simctl launch booted co.swipelab.m3te
+sleep 2
 xcrun simctl io booted screenshot /tmp/m3te.png
 ```
 
+> **Render-readiness wait — applies to every sim capture recipe in this README.**
+> Each deterministic section below shows only the pinned `launch` command (it swaps a
+> different scene in for the `launch` line above); capture it exactly as here — after
+> the launch, **wait for the first rendered frame** (`sleep 2`, or poll the
+> screenshot) **before** `xcrun simctl io booted screenshot`. Skipping the wait
+> captures the white launch screen, not the board.
+
 The screenshot should match `goldens/p6_idle_t0.png` (the resting candy board),
 modulo the status-bar clock — pixel-exact equality is not required; compare the
 board + HUD region, not the top status strip. A tap selects a cell; a swipe