enforce mandatory X-Session-Id header for access token validation

Session binding was bypassable: if the X-Session-Id header was absent,
validate_token skipped the check entirely, allowing a stolen JWT to be
used without the originating session.

Server-side: reject 401 early in Flask middleware and daemon WebSocket
handler when X-Session-Id is missing, before calling validate_token.
Updated validate_token to always enforce session_id matching for access
tokens (refresh tokens are unaffected as they carry no session_id claim).

Frontend: removed dead if (stored.session_id) guards in api.js since
the header is now always required. Added X-Session-Id to logout request
headers and always store session_id on login/refresh.

webui/static/hoover/components/auth.js

@@ -67,6 +67,7 @@ export async function logout() {
                 'Content-Type': 'application/json',
                 'Accept': 'application/json',
                 'Authorization': 'Bearer ' + token,
+                'X-Session-Id': sessionStorage.getItem('vw:session_id'),
             };
             const refresh = sessionStorage.getItem('vw:refresh');
             await fetch('/api/auth/logout', {
@@ -120,9 +121,7 @@ export function handleLoginSuccess(data, redirectPath = '/dashboard') {
         setAuthToken(tokens.access_token);
         sessionStorage.setItem('vw:refresh', tokens.refresh_token);
         sessionStorage.setItem('vw:access_ttl', String((data.access_ttl || 300) * 1000));
-        if (tokens.session_id) {
-            sessionStorage.setItem('vw:session_id', tokens.session_id);
-        }
+        sessionStorage.setItem('vw:session_id', tokens.session_id);
         if (user) {
             sessionStorage.setItem('vw:user', JSON.stringify(user));
             if (permissions) {