Wire language switcher into Settings; add E2E UAT suite

- App.svelte: language toggle (EN/BM) wired to existing i18n.js store,
  header tagline reflects selection. Was previously dead code with no
  UI control (found by e2e-uat.cjs during full-flow UAT).
- e2e-uat.cjs: Playwright-driven E2E UAT against the live deployment —
  real clicks/typing through all 7 tabs, faraid textbook-case
  verification, heir-exclusion blocking, marad al-mawt guard, 1/3 cap
  override flow, claim issuance/transfer, export/delete-all guards,
  PWA and console-error checks.

package.json

@@ -12,6 +12,7 @@
   },
   "devDependencies": {
     "@sveltejs/vite-plugin-svelte": "^5.0.3",
+    "playwright": "^1.62.1",
     "svelte": "^5.20.0",
     "vite": "^6.2.0"
   },