feat(android): blue instead of cyan, everywhere at once

Cyan came from the desktop app. On the phone the reference is the system: its global search and its own apps are blue, and an app should look like the place it runs.

Accent #3B82F6 on the same slate, with white on the accent since blue is darker than cyan. The launcher icon and the launch screen follow - a cyan padlock in front of a blue interface would have read as a different app.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

android-client/android-res/drawable/splash_vector.xml

@@ -10,13 +10,13 @@
     android:viewportWidth="288"
     android:viewportHeight="288">
     <path
-        android:strokeColor="#22D3EE"
+        android:strokeColor="#3B82F6"
         android:strokeWidth="11"
         android:strokeLineCap="round"
         android:fillColor="#00000000"
         android:pathData="M124,139 L124,121 A20,20 0 0 1 164,121 L164,139" />
     <path
-        android:fillColor="#22D3EE"
+        android:fillColor="#3B82F6"
         android:pathData="M112,135 L176,135 A8,8 0 0 1 184,143 L184,179 A8,8 0 0 1 176,187 L112,187 A8,8 0 0 1 104,179 L104,143 A8,8 0 0 1 112,135 Z" />
     <path
         android:fillColor="#0F172A"