feat: add comprehensive E2E test suite (Playwright + WireGuard + API)

Adds tests/e2e/ with three layers of E2E coverage:
- API layer (tests/e2e/api/): unauthenticated access, admin endpoints,
  peer endpoints, access control enforcement — 24 tests
- Playwright UI (tests/e2e/ui/): login flows, admin navigation, peer
  dashboard/services, role-based ACL, password change — 60+ tests
- WireGuard connectivity (tests/e2e/wg/): tunnel up/down, DNS resolution
  through VPN, service ACL enforcement via iptables, full-tunnel routing
Shared helpers: PicAPIClient, WGInterface, playwright_login, cleanup.
Makefile targets: test-e2e-api, test-e2e-ui, test-e2e-wg, test-e2e.
Adds scripts/reset_admin_password.py for test bootstrap.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/e2e/helpers/cleanup.py

@@ -0,0 +1,9 @@
+def delete_e2e_peers(admin_client, prefix='e2etest-'):
+    r = admin_client.get('/api/peers')
+    if r.status_code != 200:
+        return
+    peers = r.json()
+    for p in peers:
+        name = p.get('peer') or p.get('name', '')
+        if name.startswith(prefix):
+            admin_client.delete(f'/api/peers/{name}')