chore: migrate from npm to bun, downgrade vite to v6

- switch to bun for faster installs (0.6s vs 23s)
- downgrade vite 7.3 -> 6.4.1 (fixes config bug)
- update .gitignore for bun and pnpm artifacts
- remove package-lock.json, add bun.lock

Author: DevanshuNEU

frontend/.gitignore

@@ -3,6 +3,11 @@ node_modules/
 .pnp
 .pnp.js
 
+# Package manager locks (using bun.lockb)
+package-lock.json
+yarn.lock
+pnpm-lock.yaml
+
 # Testing
 coverage/
 
@@ -30,7 +35,14 @@ Thumbs.db
 npm-debug.log*
 yarn-debug.log*
 yarn-error.log*
+pnpm-debug.log*
 
 # Vite
 .vite/
+*.local
+
+# Bun
+.bun/
+
+# Vercel
 .vercel