chore(vercel): add vercel.json build config and ensure .vercel is gitignored

* apps/landing/vercel.json: Next.js build config (framework, outputDirectory, buildCommand, installCommand) — untracked since 2025-06-18, now committed so Vercel can read it from the repo.

* .gitignore: ensure .vercel is ignored (already had .vercel/ entry; this adds the bare .vercel form for completeness).

Pair with vercel link to forgedfromwood/organoid-symbionts (production URL: https://organoid-symbionts-forgedfromwood.vercel.app).

Author: Codex

.gitignore

@@ -201,3 +201,4 @@ onchain-cache/
 
 # Optional: generated snapshots (keep canonical snapshots in repo)
 snapshots-generated/
+.vercel

apps/landing/vercel.json

@@ -0,0 +1,6 @@
+{
+  "framework": "nextjs",
+  "outputDirectory": ".next",
+  "buildCommand": "pnpm run build",
+  "installCommand": "pnpm install"
+}