identity: shared M3 Expressive theme factory + nav slide spec

FloretExpressiveTheme(lightScheme, darkScheme, darkTheme, dynamicColor,
typography) holds the family's theme mechanics — dynamic-colour resolution
(API 31+), system light/dark fallback, and the STANDARD motion scheme — while
each app supplies its own seed-derived colour schemes, so the look stays
per-app and the machinery is shared. rememberNavSlideSpec() shares the fast
spatial nav slide. android-library, Compose-only.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

identity/src/main/kotlin/de/jeanlucmakiola/floret/identity/NavTransitions.kt

@@ -0,0 +1,19 @@
+package de.jeanlucmakiola.floret.identity
+
+import androidx.compose.animation.core.FiniteAnimationSpec
+import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.unit.IntOffset
+
+/**
+ * The horizontal slide spec for screen-to-screen navigation: the *fast*
+ * spring-physics spec from the active motion scheme — snappy with a subtle
+ * springy settle, rather than a fixed easing curve. Shared so the family's apps
+ * move the same way. Read in composable scope so the non-composable `NavHost`
+ * transition lambdas can capture it.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun rememberNavSlideSpec(): FiniteAnimationSpec<IntOffset> =
+    MaterialTheme.motionScheme.fastSpatialSpec()

identity/src/main/kotlin/de/jeanlucmakiola/floret/identity/Theme.kt

@@ -0,0 +1,52 @@
+package de.jeanlucmakiola.floret.identity
+
+import android.os.Build
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.material3.ColorScheme
+import androidx.compose.material3.ExperimentalMaterial3ExpressiveApi
+import androidx.compose.material3.MaterialExpressiveTheme
+import androidx.compose.material3.MotionScheme
+import androidx.compose.material3.Typography
+import androidx.compose.material3.dynamicDarkColorScheme
+import androidx.compose.material3.dynamicLightColorScheme
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.platform.LocalContext
+
+/**
+ * The family's Material 3 Expressive theme factory. Honours system light/dark
+ * and Material You dynamic colour (API 31+), falling back to the app-supplied
+ * [lightScheme] / [darkScheme] otherwise. Routes all component + custom motion
+ * through `MaterialTheme.motionScheme` with the **standard** scheme — spring
+ * choreography without the overshoot, the family's deliberate motion choice.
+ *
+ * The mechanics are shared; the look is not. Each app keeps its identity by
+ * passing its own hand-tuned, seed-derived [lightScheme] / [darkScheme] and an
+ * optional [typography]. A thin per-app wrapper (e.g. `AgendulaTheme`) supplies
+ * those and forwards [darkTheme] / [dynamicColor] from settings.
+ */
+@OptIn(ExperimentalMaterial3ExpressiveApi::class)
+@Composable
+fun FloretExpressiveTheme(
+    lightScheme: ColorScheme,
+    darkScheme: ColorScheme,
+    darkTheme: Boolean = isSystemInDarkTheme(),
+    dynamicColor: Boolean = true,
+    typography: Typography = Typography(),
+    content: @Composable () -> Unit,
+) {
+    val colorScheme = when {
+        dynamicColor && Build.VERSION.SDK_INT >= Build.VERSION_CODES.S -> {
+            val ctx = LocalContext.current
+            if (darkTheme) dynamicDarkColorScheme(ctx) else dynamicLightColorScheme(ctx)
+        }
+        darkTheme -> darkScheme
+        else -> lightScheme
+    }
+
+    MaterialExpressiveTheme(
+        colorScheme = colorScheme,
+        typography = typography,
+        motionScheme = MotionScheme.standard(),
+        content = content,
+    )
+}