feat: phase 2 databases via DBX (v0.3.0)

- dbx-mcp persistent stdio subprocess in Go backend (internal/dbx),
  lazy start + single retry, tool failures surface as 502
- core.db_connections registry: per-project connections, credentials
  server-side only, managed entries protected (409)
- platform-postgres + platform-dragonfly auto-register per project
- REST proxy: list/create/delete/test, databases, tables, describe,
  schema context, SQL query, redis command
- Databases page: connection list, schema/table browser, column
  inspector, SQL editor with result grid + row detail, redis console
- backend image moved to debian-slim for glibc; pinned dbx release
  with SHA256 verification

Authored By: TDvorak <[email protected]>

apps/frontend/src/App.tsx

@@ -39,6 +39,7 @@ import {
   AuthPage,
   type AuthUser,
   CollectionsPage,
+  DatabasesPage,
   LoginPage,
   MembersPage,
   ProjectsPage,
@@ -51,6 +52,7 @@ import {
   IconProjects,
   IconMembers,
   IconStorage,
+  IconDatabases,
   IconCollections,
   IconAudit,
   IconAuth,
@@ -1408,6 +1410,7 @@ export default function App() {
     { id: "nav-dashboard", label: "Go to Overview", category: "Navigate", icon: <IconOverview class="w-4 h-4" />, keywords: ["home", "dashboard"], action: () => setActiveView("dashboard") },
     { id: "nav-projects", label: "Go to Projects", category: "Navigate", icon: <IconProjects class="w-4 h-4" />, keywords: ["project"], action: () => setActiveView("projects") },
     { id: "nav-members", label: "Go to Members", category: "Navigate", icon: <IconMembers class="w-4 h-4" />, keywords: ["team", "users", "invite"], action: () => setActiveView("members") },
+    { id: "nav-databases", label: "Go to Databases", category: "Navigate", icon: <IconDatabases class="w-4 h-4" />, keywords: ["db", "sql", "query", "tables", "redis"], action: () => setActiveView("databases") },
     { id: "nav-storage", label: "Go to Storage", category: "Navigate", icon: <IconStorage class="w-4 h-4" />, keywords: ["files", "buckets", "upload"], action: () => setActiveView("storage") },
     { id: "nav-collections", label: "Go to Collections", category: "Navigate", icon: <IconCollections class="w-4 h-4" />, keywords: ["documents", "database"], action: () => setActiveView("collections") },
     { id: "nav-auth", label: "Go to Authentication", category: "Navigate", icon: <IconAuth class="w-4 h-4" />, keywords: ["users", "sign in", "ban"], action: () => setActiveView("auth") },
@@ -1613,6 +1616,14 @@ export default function App() {
             />
           </Show>
 
+          <Show when={activeView() === "databases"}>
+            <DatabasesPage
+              projectID={activeProject()?.id}
+              canManage={canUpdateProject()}
+              demoMode={isDemo}
+            />
+          </Show>
+
           <Show when={activeView() === "storage"}>
             <StoragePage
               buckets={buckets()}