refactor: rename apps/ to clients/ + update architecture docs

Rename apps/ → clients/ for clarity:
- app/ (singular) = Python backend (FastAPI, server-rendered web UI)
- clients/ (plural) = standalone client applications (API consumers)

The web storefront/store/admin stays in app/ because it's server-
rendered Jinja2, not a standalone frontend. clients/ is for native
apps that connect to the API externally.

Updated:
- docs/architecture/overview.md — added clients/ to project structure
- clients/terminal-android/SETUP.md — updated path references

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

clients/terminal-android/app/src/main/res/values/themes.xml

@@ -0,0 +1,5 @@
+<resources>
+    <style name="Theme.RewardFlowTerminal" parent="Theme.Material3.DayNight.NoActionBar">
+        <item name="android:windowFullscreen">true</item>
+    </style>
+</resources>