chore(ci): add frontend boundary tripwire script

Grep-based tripwire flagging multi-type includeItemTypes literals in the
Svelte frontend — the machine-detectable signature of the item-type
taxonomy leaking into presentation. Wire it into the Gitea build-and-test
workflow and a check:boundary package script. Motivated by
docs/specs/scoped-search-boundary.md.

package.json

@@ -17,6 +17,7 @@
     "test:e2e:dev": "wdio run ./wdio.conf.ts --watch",
     "test:all": "./scripts/test-all.sh",
     "test:rust": "./scripts/test-rust.sh",
+    "check:boundary": "bash scripts/check-frontend-boundary.sh",
     "android:build": "./scripts/build-android.sh",
     "android:build:release": "./scripts/build-android.sh release",
     "android:build:clean": "rm -rf node_modules/.vite dist .svelte-kit .next build target src-tauri/target && bun install && bun run build",