fix(setup,ui): risolve errori setup + logo SVG theme-aware

- setup: corregge path templates (sibling di api/, non figlio) e firma TemplateResponse
- setup: invalida sessione client dopo operazioni che ruotano l'API key (init DB, creazione admin, cambio password, attivazione utente)
- api_client: include il nome del campo nei messaggi di errore 422 (FastAPI validation)
- ui: nuovo componente _app_logo.html (SVG inline theme-aware) usato su login e navbar

src/backend/templates/setup/setup.html

@@ -559,6 +559,19 @@
         return data;
     }
 
+    /* Setup operations rotate api_keys (DB init, admin creation, password
+     * change, user (de)activation). Any Flask session held in this browser
+     * still carries the old key, so we clear it to force a fresh /auth/login. */
+    async function invalidateClientSession() {
+        try {
+            await fetch('/auth/logout', {
+                method: 'POST',
+                credentials: 'same-origin',
+                redirect: 'manual',
+            });
+        } catch (_) { /* best-effort */ }
+    }
+
     /* ------------------------------------------------------------------ */
     /* Check DB status                                                     */
     /* ------------------------------------------------------------------ */
@@ -635,6 +648,7 @@
         try {
             const data = await apiPost('/init-db', { password: setupPassword });
             showToast(data.message, 'success');
+            await invalidateClientSession();
             await checkStatus();
         } catch (e) {
             showToast(e.message, 'error');
@@ -667,6 +681,7 @@
                 admin_display_name: display,
             });
             showToast(data.message, 'success');
+            await invalidateClientSession();
             // Clear form
             document.getElementById('admin-username').value = '';
             document.getElementById('admin-password').value = '';
@@ -690,6 +705,7 @@
             if (data.measurements_created) msg += ', measurements: ' + data.measurements_created;
             msg += ')';
             showToast(msg, 'success');
+            await invalidateClientSession();
             await loadUsers();
         } catch (e) {
             showToast(e.message, 'error');
@@ -876,6 +892,7 @@
             if (pwd) body.user_password = pwd;
             var data = await apiPost('/manage-user', body);
             showToast(data.message, 'success');
+            await invalidateClientSession();
             closeModal('modal-user');
             await loadUsers();
         } catch (e) {
@@ -908,6 +925,7 @@
                 new_password: newPwd,
             });
             showToast(data.message, 'success');
+            await invalidateClientSession();
             closeModal('modal-password');
         } catch (e) {
             showToast(e.message, 'error');
@@ -924,6 +942,7 @@
                 user_id: userId,
             });
             showToast(data.message, 'success');
+            await invalidateClientSession();
             await loadUsers();
         } catch (e) {
             showToast(e.message, 'error');