refactor(decnet_web/Config): extract types

Foundation for the Config split. UserEntry / ConfigData move out
of the page so the upcoming hook + tab extractions can import
without reaching back through Config.tsx. New ConfigTab union and
FormMsg type for the inline success/error chip pattern that
repeats across every admin form on the page.

- New Config/types.ts (UserEntry, ConfigData, ConfigTab, FormMsg)
- Config.tsx loses the inline interfaces and the `as any` cast on
  setActiveTab in the tab-switcher.

decnet_web/src/components/Config/types.ts

@@ -0,0 +1,27 @@
+/** Wire + UI types for the Config page surface. */
+
+export interface UserEntry {
+  uuid: string;
+  username: string;
+  role: string;
+  must_change_password: boolean;
+}
+
+export interface ConfigData {
+  role: string;
+  deployment_limit: number;
+  global_mutation_interval: string;
+  users?: UserEntry[];
+  developer_mode?: boolean;
+}
+
+/** Inline success/error chip surfaced under each form section. */
+export type FormMsg = { type: 'success' | 'error'; text: string };
+
+export type ConfigTab =
+  | 'limits'
+  | 'users'
+  | 'globals'
+  | 'appearance'
+  | 'workers'
+  | 'ttp';