fix: valid HF Space colorTo value (black → gray)

HF only accepts: red, yellow, green, blue, indigo, purple, pink, gray

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -2,7 +2,7 @@
 title: HuggingClip
 emoji: 📎
 colorFrom: gray
-colorTo: black
+colorTo: gray
 sdk: docker
 app_port: 7861
 pinned: true