Add vue-router, login/setup flow and backend logging

Refactor frontend to route-based navigation with vue-router, add
system setup and login pages with API integration. Add structured
logging, access-log middleware and startup lifecycle to FastAPI
backend.

web/src/assets/styles/views/login-view.css

@@ -482,6 +482,16 @@
   margin-top: 2px;
 }
 
+.login-error {
+  padding: 12px 14px;
+  border: 1px solid rgba(239, 68, 68, .18);
+  border-radius: 8px;
+  background: #fef2f2;
+  color: #b91c1c;
+  font-size: 13px;
+  line-height: 1.55;
+}
+
 .remember {
   display: inline-flex;
   align-items: center;
@@ -528,6 +538,13 @@
   background: linear-gradient(135deg, #13c990, #047857);
 }
 
+.submit-btn:disabled,
+.sso-btn:disabled {
+  opacity: .6;
+  cursor: not-allowed;
+  box-shadow: none;
+}
+
 .divider {
   position: relative;
   display: grid;