Add Playwright E2E harness for the RDM audit workspace

Why: U4 acceptance requires real-browser runs of the trace/audit
workspace; the repo had only a manual .playwright.ts stub gated on
PLAYWRIGHT_BASE_URL with no config, deps, or service wiring.

Evidence: config/deps/spec staged; full run driven by Dev-side
scripts/e2e.sh (seed-only smoke in progress in this task branch).

Impact: dev-only additions (@playwright/test devDep, preview proxy
segment, e2e/rdm-audit.playwright.ts); no production bundle changes.

Refs: Dev task feature/rdm-e2e-acceptance; U4 in
modules/documents/docs/proposals/2026-10-11-rdm-two-trees-trace-audit-integration.md

package.json

@@ -7,7 +7,8 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "test": "vitest run",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "e2e": "playwright test"
   },
   "dependencies": {
     "docx-preview": "^0.4.1",
@@ -21,6 +22,7 @@
     "xlsx": "^0.18.5"
   },
   "devDependencies": {
+    "@playwright/test": "^1.50.1",
     "@types/node": "^22.20.4",
     "@types/react": "^19.2.0",
     "@types/react-dom": "^19.2.0",