Add app icon and asset support

- clock.png (10x10) set as fap_icon for app browser
- app_icon.png (47x39) compiled as I_app_icon_47x39 asset for in-app use
- Include digital_alarm_clock_icons.h in source

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EYNXvRg4xjHHE9oPH9kYYU

application.fam

@@ -9,5 +9,6 @@ App(
     fap_description="Nightstand-style clock with configurable alarm, vibrate, and buzzer.",
     fap_author="",
     fap_weburl="",
+    fap_icon="assets/clock.png",
     fap_icon_assets="assets",
 )