feat(maestro): match activity rail blink/flash to web timings

Replaces the tween/Reverse pulse with keyframe animations mirroring
web/src/components/sidebar/sidebar.css exactly: a hard 1200ms on/off
blink for AwaitingInput (steps(1), no crossfade) and a 1400ms
ease-out double-flash for Error.

android/app/src/main/java/pt/naps/maestro/ui/sidebar/ActivityRail.kt

@@ -2,12 +2,12 @@ package pt.naps.maestro.ui.sidebar
 
 import androidx.compose.animation.animateColorAsState
 import androidx.compose.animation.core.InfiniteTransition
-import androidx.compose.animation.core.LinearEasing
+import androidx.compose.animation.core.LinearOutSlowInEasing
 import androidx.compose.animation.core.RepeatMode
 import androidx.compose.animation.core.animateFloat
 import androidx.compose.animation.core.infiniteRepeatable
+import androidx.compose.animation.core.keyframes
 import androidx.compose.animation.core.rememberInfiniteTransition
-import androidx.compose.animation.core.tween
 import androidx.compose.foundation.background
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.fillMaxHeight
@@ -52,18 +52,51 @@ fun activityStateWord(activity: ActivityState): String =
         ActivityState.Error -> "Error"
     }
 
-/** A held bar that pulses its alpha between 1 and [minAlpha] every
- * [periodMs] — the blink/flash motion `AwaitingInput`/`Error` earn. */
+/** A hard on/off blink, one cycle per 1200ms — mirrors the web rail's
+ * `maestro-rail-blink` keyframes (docs/SIDEBAR.md, web/src/components/sidebar/sidebar.css):
+ * held at full alpha for the first half of the cycle, then snapped to 0 for
+ * the second half, with no crossfade. */
 @Composable
-private fun InfiniteTransition.pulsingAlpha(minAlpha: Float, periodMs: Int): Float {
+private fun InfiniteTransition.blinkAlpha(): Float {
     val alpha by animateFloat(
         initialValue = 1f,
-        targetValue = minAlpha,
+        targetValue = 0f,
         animationSpec = infiniteRepeatable(
-            animation = tween(durationMillis = periodMs, easing = LinearEasing),
-            repeatMode = RepeatMode.Reverse,
+            animation = keyframes {
+                durationMillis = 1200
+                1f at 0
+                1f at 599
+                0f at 600
+                0f at 1199
+            },
+            repeatMode = RepeatMode.Restart,
         ),
-        label = "activity-rail-alpha",
+        label = "activity-rail-blink",
+    )
+    return alpha
+}
+
+/** A fast double-flash every 1400ms — mirrors the web rail's
+ * `maestro-rail-flash` keyframes: two dips to quarter alpha early in the
+ * cycle, then held at full alpha for the remainder. */
+@Composable
+private fun InfiniteTransition.flashAlpha(): Float {
+    val alpha by animateFloat(
+        initialValue = 1f,
+        targetValue = 1f,
+        animationSpec = infiniteRepeatable(
+            animation = keyframes {
+                durationMillis = 1400
+                1f at 0 using LinearOutSlowInEasing
+                0.25f at 210 using LinearOutSlowInEasing
+                1f at 420 using LinearOutSlowInEasing
+                0.25f at 630 using LinearOutSlowInEasing
+                1f at 840 using LinearOutSlowInEasing
+                1f at 1400
+            },
+            repeatMode = RepeatMode.Restart,
+        ),
+        label = "activity-rail-flash",
     )
     return alpha
 }
@@ -77,8 +110,8 @@ fun ActivityRail(activity: ActivityState, modifier: Modifier = Modifier) {
     val color by animateColorAsState(targetValue = activityColor(activity), label = "activity-rail-color")
     val infinite = rememberInfiniteTransition(label = "activity-rail-motion")
     val alpha = when (activity) {
-        ActivityState.AwaitingInput -> infinite.pulsingAlpha(minAlpha = 0.35f, periodMs = 600)
-        ActivityState.Error -> infinite.pulsingAlpha(minAlpha = 0.25f, periodMs = 220)
+        ActivityState.AwaitingInput -> infinite.blinkAlpha()
+        ActivityState.Error -> infinite.flashAlpha()
         else -> 1f
     }
     Box(