fix(api): keep tsx in devDependencies to match lockfile

Frozen-lockfile installs on Vercel/CI rejected the previous move of tsx to
runtime deps. Nixpacks/Vercel retain devDeps in node_modules after install,
so tsx is still resolvable at runtime via `pnpm --filter @sheetforge/api start`.

Author: Devansh-365

apps/api/package.json

@@ -16,7 +16,6 @@
   "dependencies": {
     "hono": "^4.6.13",
     "@hono/node-server": "^1.13.7",
-    "tsx": "^4.19.2",
     "zod": "^3.24.2",
     "@sheetforge/queue": "workspace:^",
     "@sheetforge/shared-db": "workspace:^",
@@ -33,6 +32,7 @@
     "@sheetforge/slice-write-queue": "workspace:^"
   },
   "devDependencies": {
-    "@types/node": "^22.10.2"
+    "@types/node": "^22.10.2",
+    "tsx": "^4.19.2"
   }
 }