feat(integrations): add Git hosting providers and Clone UI

Add integrations for GitHub, GitLab (cloud & self-hosted), Azure DevOps,
and Gitea, storing personal access tokens in the operating system
keychain. Azure DevOps supports multiple independently configurable
organizations, and the Clone → Integrations tab loads, filters, sorts,
and clones repositories using stored credentials. Update the API
contract, help overlay, README, changelog, and application version
metadata to document and ship the feature.

- Add list_integration_repositories API command and related types
- New Clone → Integrations UI with search, refresh, and direct clone
- Store tokens in OS keychain and support multiple Azure DevOps orgs

docs/api-contract.md

@@ -101,6 +101,20 @@ interface GitLfsFile {
   oid: string;
   version: string;
 }
+
+type GitIntegrationProvider = "github" | "gitlab" | "gitlab-self-hosted" | "azure-devops" | "gitea";
+
+interface IntegrationRepository {
+  id: string;
+  name: string;
+  fullName: string;
+  description: string;
+  cloneUrl: string;
+  sshUrl: string;
+  webUrl: string;
+  updatedAt: string;
+  private: boolean;
+}
 ```
 
 ## Commands
@@ -110,6 +124,7 @@ The command list below includes the repository-management and synchronization AP
 - `open_repository(path: string): Promise<GitStatus>`
 - `init_repository(path: string, initialBranch?: string): Promise<GitStatus>`
 - `clone_repository(...): Promise<RepositoryBundle>`
+- `list_integration_repositories(provider: GitIntegrationProvider, baseUrl: string, accountId?: string): Promise<IntegrationRepository[]>`; loads credentials from the operating system keychain and returns every repository accessible through the configured Git hosting account.
 - `get_status(path: string): Promise<GitStatus>`
 - `git_lfs_status(path: string): Promise<GitLfsStatus>`
 - `git_lfs_install(path: string): Promise<GitLfsStatus>`