hive-forge: pr edit --base retargets a PR

Forgejo's issue edit endpoint (/issues/<n>) has no base field, so `pr edit`
could not retarget a stacked PR once its base merged. `--base <BRANCH>`
(non-empty) switches the edit onto PATCH /pulls/<n>, which carries `base`
alongside title/body/state/milestone. Without `--base`, `pr edit` is
unchanged and still goes through the issue endpoint.

hive-forge/src/verbs/mod.rs

@@ -34,6 +34,7 @@ pub mod pr_assign_reviewer;
 pub mod pr_cmd;
 pub mod pr_commits;
 pub mod pr_create;
+pub mod pr_edit;
 pub mod pr_merge;
 pub mod pr_reviews;
 pub mod pr_status;