refactor: remove pearl from PearlShell 3D scene

[koishi510]

Remove pearl mesh, point light, and all related animations (visibility, opacity, pulse) from the shell gesture component.

Related Issue

Summary

Change Type

• New Feature (feat)
• Bug Fix (fix)
• Refactoring (refactor)
• Documentation (docs)
• Dependency / Configuration (chore)

Self-Check Checklist

Backend (Go):

• go build ./... passes
• go vet ./... passes
• gofmt produces no diff

Frontend (Vue):

• npm run lint passes
• npm run typecheck passes

General:

• Removed all temporary debug output
• No sensitive data in the code

Test Steps

1. Pull branch and install dependencies:

   cd backend && go mod download
   cd ../frontend && npm install

2. Start the application:

   make dev-backend    # Terminal 1
   make dev-frontend   # Terminal 2

3. Verification steps:
   • ...