chore(frontend): switch to bun (remove pnpm/node refs) (#7)

* chore(frontend): remove pnpm packageManager declaration

Bun is the canonical frontend package manager (bun.lock, bunfig.toml,
bun test). The leftover packageManager: pnpm@10.30.3 field caused
corepack to enforce pnpm, conflicting with bun-first workflow.

fn-17-switch-frontend-to-bun-remove-pnpmnode.1

* chore(frontend): remove vestigial vitest.config.ts

No vitest package is installed and no source file imports from
vitest. bun test is the canonical test runner (configured via
bunfig.toml preload + @happy-dom/global-registrator).

Verified: bun run typecheck ✓ | bun run build ✓ | bun test ✓ (10 pass) | bun run dev ✓

fn-17-switch-frontend-to-bun-remove-pnpmnode.2

Author: z23cc

frontend/package.json

@@ -13,7 +13,6 @@
   "keywords": [],
   "author": "",
   "license": "ISC",
-  "packageManager": "pnpm@10.30.3",
   "dependencies": {
     "@xyflow/react": "^12.10.2",
     "lucide-react": "^1.7.0",