Doodle-jump camera and remove player shadow

- Camera now uses a trigger line at 42% from top. Player rises/falls
  freely below the line; camera only scrolls up past it, never down.
- Remove playerShadow graphics that followed the hero around.
- Ignore .vercel-cli-config (CLI auth cache used as Windows workaround).

.gitignore

@@ -35,3 +35,6 @@ rocket_preview.png
 
 # Agent notes — local only, useful for AI sessions but not for public repo
 AGENTS.md
+
+# Vercel CLI auth cache (workaround for Windows EXDEV issue)
+.vercel-cli-config/