chore: migrate from pnpm to bun package manager

Switch package manager from pnpm to bun for faster dependency
installation and better monorepo support. Remove pnpm-specific
configuration files and update all scripts to use bun commands.

bunfig.toml

@@ -0,0 +1,13 @@
+# Bunfig - Bun 套件優化配置
+# https://bun.sh/docs/runtime/bunfig
+
+[install]
+# 使用精確版本，避免意外升級
+exact = true
+
+# 生產環境使用 lockfile
+frozenLockfile = true
+
+[install.lockfile]
+# 保存 lockfile
+save = true