feat: loading overlay on dashboard, RDP pooled session routing fix

- dashboard.html: overlay div moved before <script> so getElementById works;
  double rAF ensures browser paints spinner before navigation
- main.py: pooled_rdp route fix — session_status now returns /svc/<slug>/
  route and redirect_url for POOL: RDP sessions (was always ready instantly)
- docker-compose.yml: parametrise env vars via .env for easier tuning

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

app/templates/dashboard.html

@@ -103,6 +103,18 @@
     </section>
     <footer class="made-by-wrap"><a class="made-by" href="mailto:rgalyaviev@mont.com">Made by Galyaviev</a></footer>
   </main>
+  <style>
+    #loading-overlay{display:none;position:fixed;inset:0;z-index:8888;background:rgba(10,18,28,.88);
+      backdrop-filter:blur(4px);flex-direction:column;align-items:center;justify-content:center;gap:1.2rem}
+    #loading-overlay .lo-spinner{width:52px;height:52px;border:4px solid rgba(220,232,245,.15);
+      border-top-color:#2a8cd6;border-radius:50%;animation:lo-spin .85s linear infinite}
+    #loading-overlay .lo-text{color:#a0b8cc;font:600 1rem sans-serif}
+    @keyframes lo-spin{to{transform:rotate(360deg)}}
+  </style>
+  <div id="loading-overlay">
+    <div class="lo-spinner"></div>
+    <div class="lo-text">Ожидайте...</div>
+  </div>
   <script>
     (function () {
       const username = {{ user.username|tojson }};
@@ -153,16 +165,30 @@
         return sp;
       }
 
+      const loadingOverlay = document.getElementById('loading-overlay');
+
       document.querySelectorAll('a.tile[href^="/go/"]').forEach(function (link) {
-        link.addEventListener('click', function () {
+        link.addEventListener('click', function (e) {
+          e.preventDefault();
+          let href = link.getAttribute('href');
           try {
-            const url = new URL(link.getAttribute('href'), window.location.origin);
+            const url = new URL(href, window.location.origin);
             const params = currentScreenParams();
             url.search = params.toString();
-            link.setAttribute('href', url.pathname + '?' + url.searchParams.toString());
+            href = url.pathname + '?' + url.searchParams.toString();
           } catch (e) {}
+          if (loadingOverlay) loadingOverlay.style.display = 'flex';
+          requestAnimationFrame(function () {
+            requestAnimationFrame(function () {
+              window.location.href = href;
+            });
+          });
         }, { capture: true });
       });
+
+      window.addEventListener('pageshow', function (e) {
+        if (loadingOverlay) loadingOverlay.style.display = 'none';
+      });
     })();
   </script>
 </body>