fix: correct env var add form action path

The 'Add' environment variable form in app_detail.html was posting to
/apps/{id}/env, but the route is registered as /apps/{id}/env-vars.
This path mismatch caused a 404 when trying to add environment variables
from the app detail page.

Fix the form action to use the correct /apps/{id}/env-vars path,
matching the route defined in routes.go.

closes #156

static/js/dashboard.js

@@ -5,17 +5,18 @@
  */
 
 document.addEventListener("alpine:init", () => {
-  Alpine.data("dashboard", () => ({
-    init() {
-      // Update relative times every minute
-      setInterval(() => {
-        this.$el.querySelectorAll("[data-time]").forEach((el) => {
-          const time = el.getAttribute("data-time");
-          if (time) {
-            el.textContent = Alpine.store("utils").formatRelativeTime(time);
-          }
-        });
-      }, 60000);
-    },
-  }));
+    Alpine.data("dashboard", () => ({
+        init() {
+            // Update relative times every minute
+            setInterval(() => {
+                this.$el.querySelectorAll("[data-time]").forEach((el) => {
+                    const time = el.getAttribute("data-time");
+                    if (time) {
+                        el.textContent =
+                            Alpine.store("utils").formatRelativeTime(time);
+                    }
+                });
+            }, 60000);
+        },
+    }));
 });