ci(web): declare the build allowlist in both places, and report pnpm's view

Third build-web failure with the same ERR_PNPM_IGNORED_BUILDS. The
setting was first in package.json (pnpm 10 here does not read it) and
then in pnpm-workspace.yaml (verified read here, still ignored on the
runner), so the runner's pnpm evidently resolves it differently and I
have been guessing at which.

Declares it in both locations -- four duplicated lines against a failure
that only manifests on CI -- and adds a step printing pnpm --version and
the resolved value, so if this still fails the log says why instead of
costing another round trip.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XZG2i4AmfSqE97EJGBVb64

web/package.json

@@ -32,5 +32,11 @@
     "typescript": "^5.9.3",
     "typescript-eslint": "^8.46.2",
     "vite": "^7.2.2"
+  },
+  "pnpm": {
+    "onlyBuiltDependencies": [
+      "@swc/core",
+      "esbuild"
+    ]
   }
 }