feat(integrations): support automatic branch cleanup after merge

Add a new git::review_cleanup module that implements a CleanupPlan with
prepare() and finish() routines to safely remove/clean tracking and local
branches after a PR/MR is merged. The cleanup logic validates branch names,
ensures a clean worktree, checks remotes/URLs, verifies commits/ancestry,
protects against concurrent worktrees or divergent local/remote commits, and
performs authenticated fetch/push and ref updates. Unit tests for the cleanup
behavior are included.

Wire provider-side cleanup into integrations:
- add an integrations/cleanup module to read provider PR payloads and derive
  cleanup inputs
- run cleanup::prepare(...) before performing a merge when an optional
  cleanup_path is provided
- after a successful provider merge, run cleanup::finish(...); any failure is
  reported as MERGE_ACCEPTED_CLEANUP_FAILED

Also:
- export the new git review_cleanup module (src-tauri/src/git.rs)
- accept an optional cleanup_path parameter in run_integration_review_action
- remove the previous REVIEW_REQUEST_TIMEOUT wrapper around the spawned
  blocking task (the integration action is no longer wrapped with the 35s timeout)

src/lib/git.ts

@@ -72,8 +72,8 @@ export function getIntegrationReviewMergeOptions(provider: GitIntegrationProvide
   return invoke("get_integration_review_merge_options", { provider, baseUrl, token, repositoryId: request.repositoryId, repositoryName: request.repositoryName });
 }
 
-export function runIntegrationReviewAction(provider: GitIntegrationProvider, baseUrl: string, username: string, token: string, request: IntegrationReviewRequest, action: IntegrationReviewAction, mergeMethod?: IntegrationMergeMethod): Promise<void> {
-  return invoke<void>("run_integration_review_action", { provider, baseUrl, username, token, repositoryId: request.repositoryId, repositoryName: request.repositoryName, number: request.number, action, mergeMethod });
+export function runIntegrationReviewAction(provider: GitIntegrationProvider, baseUrl: string, username: string, token: string, request: IntegrationReviewRequest, action: IntegrationReviewAction, mergeMethod?: IntegrationMergeMethod, cleanupPath?: string): Promise<void> {
+  return invoke<void>("run_integration_review_action", { provider, baseUrl, username, token, repositoryId: request.repositoryId, repositoryName: request.repositoryName, number: request.number, action, mergeMethod, cleanupPath });
 }
 
 export function getIntegrationReviewDetails(provider: GitIntegrationProvider, baseUrl: string, username: string, token: string, request: IntegrationReviewRequest): Promise<IntegrationReviewRequest> {