Android: add the in-app "Reduce motion in NOOP" toggle as a third rememberPoseStill() signal #941

Follow-up to #931, which adds a third motion signal on the Apple side only. Filed because #931's description originally claimed this Kotlin pref already existed — it does not, and that wording is corrected there.

The asymmetry

After #931 lands, the two gates read differently:

fun rememberPoseStill(): Boolean = rememberReduceMotion() || rememberPowerSaveMode()

The first two signals reached parity in #909 / #911. The third — an in-app toggle, default OFF — is the one that is Apple-only, and it is the signal the user who asked for this actually wanted: a way to quiet the app without putting the whole phone into battery saver.

What the Android side needs

1. A pref. NoopPrefs (android/app/src/main/java/com/noop/ui/MainActivity.kt:163) stores keys as KEY_* constants, so this should be const val KEY_QUIET_MOTION = "noop.quietMotion" — note the key string is the cross-platform contract and must match the Apple @AppStorage key noop.quietMotion exactly, so a .noopbak round-trip carries the setting across platforms. (Worth saying plainly: the correct Kotlin spelling is NoopPrefs.KEY_QUIET_MOTION, not NoopPrefs.quietMotion — the latter is the name Make Low Power Mode mean "stop everything decorative", and stop the tilt sensor (#909) #931 wrongly claimed already existed, and it does not match this file's convention either.)
2. A third term in the gate, read live rather than once — the Apple side uses UserDefaults.didChangeNotification so flipping the toggle poses the surfaces without leaving the screen; Android needs the SharedPreferences equivalent, for the same reason ACTION_POWER_SAVE_MODE_CHANGED is already observed.
3. A Settings toggle, default OFF, under the Appearance section, with the string translated into the catalog locales.
4. Update PoseStillCoverageTest. android/app/src/test/java/com/noop/ui/PoseStillCoverageTest.kt:112 currently pins the exact two-signal source line:

   code.contains("fun rememberPoseStill(): Boolean = rememberReduceMotion() || rememberPowerSaveMode()")

   That assertion will fail the moment the third signal is added, which is the test working correctly — it is a census of the gate's shape, and the shape is changing. The Apple twin (QuietMotionCoverageTests.testGateReadsAllThreeSignalsAndStaysLive) is the model for what it should assert afterwards: that all three signals are OR-ed and that each stays live, because losing one signal is invisible in the app — the screen looks right in whichever mode still works.

Not in scope here

The LiquidMotion half of #931 (stopping the decorative 60 Hz CMMotionManager feed at the app boundary) has no Android twin to fix: there is no equivalent decorative sensor loop on that side. This issue is only the third gate signal and its toggle.