Add multi-database discovery and grouping features

This update introduces optional automatic discovery and onboarding of all databases on a PostgreSQL instance. It also enhances the frontend UI with grouped target display and navigation, making it easier to view and manage related databases. Additionally, new backend endpoints and logic ensure seamless integration of these features.

frontend/src/styles.css

@@ -497,6 +497,36 @@ button {
   transition: transform 0.16s ease, border-color 0.16s ease, box-shadow 0.16s ease;
 }
 
+.dashboard-target-group {
+  grid-template-columns: 1fr auto;
+}
+
+.dashboard-group-list {
+  grid-column: 1 / -1;
+  display: grid;
+  gap: 8px;
+  margin-top: 2px;
+  padding-top: 8px;
+  border-top: 1px solid #264b76;
+}
+
+.dashboard-group-item {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 10px;
+  padding: 8px 10px;
+  border-radius: 10px;
+  border: 1px solid #2b5483;
+  background: #0c2344;
+}
+
+.dashboard-group-item > div {
+  display: inline-flex;
+  align-items: center;
+  gap: 8px;
+}
+
 .dashboard-target-card:hover {
   transform: none;
   border-color: #3f79af;
@@ -1813,6 +1843,11 @@ select:-webkit-autofill {
   flex-wrap: wrap;
 }
 
+.target-db-switcher {
+  max-width: 420px;
+  margin-bottom: 10px;
+}
+
 .owner-pill {
   display: inline-flex;
   align-items: center;