feat(settings): optional "Calendar" launcher name (#44)

Add a Settings → Appearance toggle that switches the app's launcher label
between "Calendula" and "Calendar", for users on launchers that can't rename
apps themselves.

The launcher entry moves off MainActivity onto two <activity-alias> components
(DefaultNameAlias / CalendarNameAlias); exactly one is enabled at a time via
PackageManager.setComponentEnabledSetting. MainActivity keeps every other intent
filter; the android.app.shortcuts meta-data moves onto both aliases so the
long-press shortcut still publishes. Component-enabled state is the single source
of truth — no persisted preference.

The ComponentName uses the applicationId for the package (carrying the
.debug/.releasetest suffix) and the namespace for the class, since manifest
".Alias" names resolve against the namespace; switching to Calendar enables the
target alias before disabling the other to avoid a zero-entry launcher transient.

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

app/src/test/java/de/jeanlucmakiola/calendula/data/appname/LauncherNameManagerTest.kt

@@ -0,0 +1,51 @@
+package de.jeanlucmakiola.calendula.data.appname
+
+import android.content.pm.PackageManager
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+/**
+ * Pure decision logic behind the app-name toggle (issue #44). The framework seam
+ * ([LauncherNameManager.set]/[current], which call `PackageManager`) is covered
+ * on-device; these tests pin the read interpretation and the write ordering.
+ */
+class LauncherNameManagerTest {
+
+    @Test
+    fun `enabled calendar alias reads as CALENDAR`() {
+        assertThat(launcherNameFor(PackageManager.COMPONENT_ENABLED_STATE_ENABLED))
+            .isEqualTo(LauncherName.CALENDAR)
+    }
+
+    @Test
+    fun `default and disabled calendar alias read as CALENDULA`() {
+        assertThat(launcherNameFor(PackageManager.COMPONENT_ENABLED_STATE_DEFAULT))
+            .isEqualTo(LauncherName.CALENDULA)
+        assertThat(launcherNameFor(PackageManager.COMPONENT_ENABLED_STATE_DISABLED))
+            .isEqualTo(LauncherName.CALENDULA)
+    }
+
+    @Test
+    fun `write plan enables the target alias before disabling the other`() {
+        val toCalendar = aliasWritePlan(LauncherName.CALENDAR)
+        assertThat(toCalendar).containsExactly(
+            AliasStateChange(LauncherAlias.CALENDAR, enabled = true),
+            AliasStateChange(LauncherAlias.DEFAULT, enabled = false),
+        ).inOrder()
+
+        val toCalendula = aliasWritePlan(LauncherName.CALENDULA)
+        assertThat(toCalendula).containsExactly(
+            AliasStateChange(LauncherAlias.DEFAULT, enabled = true),
+            AliasStateChange(LauncherAlias.CALENDAR, enabled = false),
+        ).inOrder()
+    }
+
+    @Test
+    fun `write plan never disables both aliases in the same step`() {
+        // The first step is always an enable, so the launcher can never observe a
+        // zero-entry transient regardless of switch direction.
+        for (target in LauncherName.entries) {
+            assertThat(aliasWritePlan(target).first().enabled).isTrue()
+        }
+    }
+}