feat: runtime config via DB — ganti VITE_URL_API_DESA_PLUS dengan proxy

- Tambah model AppConfig (key-value) ke schema + migration
- Tambah GET/PUT /api/admin/config (DEVELOPER only)
- Tambah proxy /api/proxy/desa-plus/* yang baca URL dari DB
- Hapus VITE_URL_API_DESA_PLUS dari frontend, ganti semua URL desa-plus ke relative proxy path
- Aktifkan Settings tab di /dev dengan UI untuk set URL_API_DESA_PLUS

URL desa-plus kini bisa diubah via /dev → Settings tanpa rebuild image.

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

src/frontend/routes/dev.tsx

@@ -113,7 +113,7 @@ const navItems = [
   // { label: 'Activity Logs', icon: TbActivity, key: 'activity-logs' },
   { label: 'Database', icon: TbDatabase, key: 'database' },
   { label: 'Project', icon: TbSitemap, key: 'project' },
-  // { label: 'Settings', icon: TbSettings, key: 'settings' },
+  { label: 'Settings', icon: TbSettings, key: 'settings' },
 ]
 
 function DevPage() {
@@ -1461,15 +1461,113 @@ function StaticFlowPanel({ graph, flowKey }: { graph: { nodes: Node[]; edges: Ed
 
 // ─── Settings Panel ────────────────────────────────────────────────────────────
 
+interface AppConfigEntry { key: string; value: string; updatedAt: string }
+
+const CONFIG_DEFINITIONS: { key: string; label: string; description: string; placeholder: string }[] = [
+  {
+    key: 'URL_API_DESA_PLUS',
+    label: 'URL API Desa Plus',
+    description: 'Base URL untuk API eksternal Desa Plus. Semua request dari frontend akan diproxy melalui server ke URL ini.',
+    placeholder: 'https://api.desa-plus.example.com',
+  },
+]
+
 function SettingsPanel() {
+  const qc = useQueryClient()
+  const [values, setValues] = useState<Record<string, string>>({})
+  const [saved, setSaved] = useState<Record<string, boolean>>({})
+
+  const { data, isLoading } = useQuery({
+    queryKey: ['admin', 'config'],
+    queryFn: () => fetch('/api/admin/config', { credentials: 'include' }).then((r) => r.json()),
+  })
+
+  const configs: AppConfigEntry[] = data?.configs ?? []
+
+  useEffect(() => {
+    const initial: Record<string, string> = {}
+    for (const def of CONFIG_DEFINITIONS) {
+      const existing = configs.find((c) => c.key === def.key)
+      initial[def.key] = existing?.value ?? ''
+    }
+    setValues(initial)
+  }, [configs])
+
+  const saveMutation = useMutation({
+    mutationFn: ({ key, value }: { key: string; value: string }) =>
+      fetch('/api/admin/config', {
+        method: 'PUT',
+        credentials: 'include',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ key, value }),
+      }).then((r) => r.json()),
+    onSuccess: (_, { key }) => {
+      qc.invalidateQueries({ queryKey: ['admin', 'config'] })
+      setSaved((prev) => ({ ...prev, [key]: true }))
+      setTimeout(() => setSaved((prev) => ({ ...prev, [key]: false })), 2000)
+    },
+  })
+
   return (
     <Stack>
       <Title order={3}>Settings</Title>
-      <Paper withBorder p="xl">
-        <Center>
-          <Text c="dimmed">Konfigurasi sistem akan ditampilkan di sini.</Text>
-        </Center>
-      </Paper>
+      <Text size="sm" c="dimmed">Konfigurasi runtime — perubahan langsung berlaku tanpa rebuild atau redeploy.</Text>
+
+      {isLoading ? <Center><Loader /></Center> : (
+        <Stack gap="md">
+          {CONFIG_DEFINITIONS.map((def) => {
+            const existing = configs.find((c) => c.key === def.key)
+            return (
+              <Paper key={def.key} withBorder p="lg" radius="md">
+                <Stack gap="xs">
+                  <Group justify="space-between" align="flex-start">
+                    <div>
+                      <Text fw={600} size="sm">{def.label}</Text>
+                      <Text size="xs" c="dimmed" ff="monospace">{def.key}</Text>
+                    </div>
+                    {existing && (
+                      <Text size="xs" c="dimmed">
+                        Diupdate {new Date(existing.updatedAt).toLocaleString('id-ID')}
+                      </Text>
+                    )}
+                  </Group>
+                  <Text size="xs" c="dimmed">{def.description}</Text>
+                  <Group gap="xs" align="flex-end">
+                    <Box style={{ flex: 1 }}>
+                      <input
+                        style={{
+                          width: '100%',
+                          padding: '8px 12px',
+                          borderRadius: 6,
+                          border: '1px solid var(--mantine-color-default-border)',
+                          background: 'var(--mantine-color-body)',
+                          color: 'var(--mantine-color-text)',
+                          fontSize: 13,
+                          fontFamily: 'monospace',
+                        }}
+                        value={values[def.key] ?? ''}
+                        onChange={(e) => setValues((prev) => ({ ...prev, [def.key]: e.target.value }))}
+                        placeholder={def.placeholder}
+                      />
+                    </Box>
+                    <Button
+                      size="sm"
+                      color={saved[def.key] ? 'green' : 'blue'}
+                      loading={saveMutation.isPending && saveMutation.variables?.key === def.key}
+                      onClick={() => saveMutation.mutate({ key: def.key, value: values[def.key] ?? '' })}
+                    >
+                      {saved[def.key] ? 'Tersimpan' : 'Simpan'}
+                    </Button>
+                  </Group>
+                  {!existing && (
+                    <Badge color="orange" variant="light" size="xs">Belum dikonfigurasi — data tidak akan ter-load</Badge>
+                  )}
+                </Stack>
+              </Paper>
+            )
+          })}
+        </Stack>
+      )}
     </Stack>
   )
 }