feat(settings): call the app "Clock" and add an app icon picker

The launcher and system label is now a plain, translatable "Clock"; the
brand name Clockula stays on the About card and in crash reports via an
untranslated app_brand_name string.

Settings → Appearance → App icon chooses between the bloom mark and a new
plain clock icon (the same dial and hands without the badge). The launcher
entry moves off MainActivity onto two <activity-alias> components, exactly
one enabled at a time, as Calendula does for its launcher name. The
component-enabled state is the single source of truth, and switching
enables the target before disabling the other so the launcher never sees
zero entries.

app/src/main/AndroidManifest.xml

@@ -77,11 +77,39 @@
             android:exported="true"
             android:launchMode="singleTop"
             android:windowSoftInputMode="adjustResize">
+            <!-- The MAIN/LAUNCHER entry lives on the two <activity-alias>
+                 below, so the launcher icon can be switched at runtime. -->
+        </activity>
+
+        <!-- The launcher entry, once per icon: exactly one alias is enabled at a
+             time, toggled from Settings → Appearance → App icon
+             (LauncherIconManager). The bloom is the manifest default. -->
+        <activity-alias
+            android:name=".BloomIconAlias"
+            android:enabled="true"
+            android:exported="true"
+            android:icon="@mipmap/ic_launcher"
+            android:label="@string/app_name"
+            android:roundIcon="@mipmap/ic_launcher_round"
+            android:targetActivity=".MainActivity">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>
-        </activity>
+        </activity-alias>
+        <activity-alias
+            android:name=".PlainIconAlias"
+            android:enabled="false"
+            android:exported="true"
+            android:icon="@mipmap/ic_launcher_plain"
+            android:label="@string/app_name"
+            android:roundIcon="@mipmap/ic_launcher_plain_round"
+            android:targetActivity=".MainActivity">
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN" />
+                <category android:name="android.intent.category.LAUNCHER" />
+            </intent-filter>
+        </activity-alias>
 
         <!-- The one exported door for android.provider.AlarmClock: every other
              app on the device drives Clockula through it. Guarded by the