Add network map UX and theme support.

Introduce network map view/components with filtering and positioning, expand contacts/map backend fields and migrations, and add a persistent light/dark theme toggle with graph label color updates for readability.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/lib/api/errors.js

@@ -0,0 +1,19 @@
+export function normalizeApiError(error) {
+  const status = error?.response?.status ?? null
+  const data = error?.response?.data
+  let message = 'Произошла ошибка запроса.'
+
+  if (typeof data === 'string' && data.trim()) {
+    message = data
+  } else if (typeof data?.error === 'string' && data.error.trim()) {
+    message = data.error
+  } else if (typeof error?.message === 'string' && error.message.trim()) {
+    message = error.message
+  }
+
+  const normalized = new Error(message)
+  normalized.status = status
+  normalized.data = data
+  normalized.original = error
+  return normalized
+}