feat(integrations): add Git hosting integrations and repo listing

Add support for integrating with external Git hosts (GitLab, Gitea,
and Azure DevOps). The backend gains a client to fetch paginated
repository lists, normalise base URLs, and surface provider errors.
Credentials are loaded from the OS keychain and a Tauri command is
exposed for the frontend to list integration repositories.

- Implement integration client with pagination, deserialization,
  and provider-specific handling.
- Centralise keychain credential loading and expose listing command.
- Update UI to manage integration metadata, persist settings, and
  save/remove tokens to the OS keychain for cloning and operations.

src/lib/types.ts

@@ -16,6 +16,57 @@ export type AppTheme = "system" | "light" | "dark";
 export type AppAppearance = "modern" | "classic" | "custom";
 export type AppLanguage = "en" | "de";
 
+export type GitIntegrationProvider = "gitlab" | "gitlab-self-hosted" | "azure-devops" | "gitea";
+
+export interface GitIntegrationConfig {
+  provider: GitIntegrationProvider;
+  enabled: boolean;
+  baseUrl: string;
+  username: string;
+  tokenStored: boolean;
+}
+
+export interface GitIntegrationSettings {
+  providers: Record<GitIntegrationProvider, GitIntegrationConfig>;
+  azureDevOpsOrganizations: AzureDevOpsOrganization[];
+}
+
+export interface AzureDevOpsOrganization {
+  id: string;
+  name: string;
+  enabled: boolean;
+  baseUrl: string;
+  username: string;
+  tokenStored: boolean;
+}
+
+export interface GitIntegrationSecretUpdate {
+  provider: GitIntegrationProvider;
+  accountId?: string;
+  token?: string;
+  removeToken?: boolean;
+}
+
+export interface GitIntegrationSource {
+  id: string;
+  provider: GitIntegrationProvider;
+  accountId?: string;
+  label: string;
+  baseUrl: string;
+}
+
+export interface GitIntegrationRepository {
+  id: string;
+  name: string;
+  fullName: string;
+  description: string;
+  cloneUrl: string;
+  sshUrl: string;
+  webUrl: string;
+  updatedAt: string;
+  private: boolean;
+}
+
 export interface CustomThemeColors {
   background: string;
   surface: string;