fix: align vercel.json with the Root Directory dashboard setting

Root-caused the actual, persistent "No Next.js version detected"
failure: it's not the package.json contents (root package.json has
declared "next" since commit 8dab8e7, and this still failed on every
single deployment since, including a genuinely fresh empty commit).
Vercel's framework/version-detection step is separate from - and runs
independently of - whatever vercel.json's custom install/build
commands do. That detection step reads package.json at the project's
configured Root Directory (a dashboard-only setting, not something
vercel.json can express), while the custom commands were separately
cd-ing into frontend/ themselves via `--dir frontend`. If Root
Directory is unset (defaults to repo root) and the repo root's
package.json lacked "next", detection fails regardless of what the
install/build commands actually did successfully.

This removes the redundant `--dir frontend` / `pnpm --dir frontend`
prefixes so the commands assume they already run from inside
frontend/ - which requires the Vercel dashboard's Root Directory
setting (Project -> Settings -> General -> Root Directory) to
actually be set to `frontend`. That dashboard change has to happen
together with this commit, not instead of it - one without the other
will still fail, just differently.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BRDH4c1gieXvgcMREtazSR

Author: christabel888

vercel.json

@@ -1,5 +1,5 @@
 {
   "framework": "nextjs",
-  "installCommand": "corepack pnpm@10.30.0 --dir frontend install --frozen-lockfile",
-  "buildCommand": "pnpm --dir frontend build"
+  "installCommand": "corepack pnpm@10.30.0 install --frozen-lockfile",
+  "buildCommand": "pnpm build"
 }