feat: Animated pixel art ocean floor background for FloatingTranscriptDebug

Replace galaxy background with animated underwater scene featuring water
depth gradient, pixel art sea floor (sand, seaweed, coral, starfish),
rising bubbles with water sway, and swimming pixel art fish. Also update
transcript-debug tool cards styling and add .claude-*/tasks/ to gitignore.

.gitignore

@@ -13,3 +13,4 @@ server/recordings/*.webm
 .claude-*/plugins/
 .claude-*/plans/
 .claude-*/file-history/
+.claude-*/tasks/