Move tar override to pnpm-workspace.yaml

pnpm v11 (installed in CI via `npm install -g pnpm`) no longer reads the
`pnpm.overrides` field from package.json, which caused
ERR_PNPM_LOCKFILE_CONFIG_MISMATCH during the frozen install. Move the
override to pnpm-workspace.yaml, the new home for the setting, so CI's
pnpm reads it and matches the lockfile.

https://claude.ai/code/session_01NPQ9AiNNnapeoTQFAR1ShY

package.json

@@ -10,10 +10,5 @@
   "dependencies": {
     "@tailwindcss/cli": "^4.1.18",
     "flowbite": "^4.0.1"
-  },
-  "pnpm": {
-    "overrides": {
-      "tar": "^7.5.11"
-    }
   }
 }

pnpm-workspace.yaml

@@ -0,0 +1,2 @@
+overrides:
+  tar: ^7.5.11