content: add Arcade Coin lock sound

Add a retro arcade coin insert sound with a two-note rising
arpeggio using square waves for 8-bit feel. Original CC0 creation.

Part of NAT-69 content catalog expansion.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

Author: tallnato

content/locksounds/arcade-coin.md

@@ -0,0 +1,10 @@
+---
+title: Arcade Coin
+author: Volts Team
+description: A retro arcade coin insert sound with a classic two-note rising arpeggio in square wave.
+tags:
+  - retro
+  - gaming
+---
+
+A retro arcade coin insert sound featuring a classic two-note rising arpeggio using square waves for that authentic 8-bit feel. Original CC0 creation.

content/locksounds/arcade-coin/arcade-coin.wav

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+title: Arcade Coin
+author: Volts Team
+description: A retro arcade coin insert sound with a classic two-note rising arpeggio in square wave.
+tags:
+  - retro
+  - gaming