fix(#1868): use HIVE_FORGE_URL for internal forge calls

Replace the hardcoded FORGE_HTTP const with forge_http_base() which
reads HIVE_FORGE_URL from the environment (already set unconditionally
by hive-c0re.nix to http://<forge.domain>). Add forge_git_url() helper
that inserts core:<token> credentials between scheme and authority for
git push/clone URLs.

All call sites updated:
- forge/mod.rs: api() OnceLock + new forge_git_url/forge_http_base fns
- forge/repos.rs: push_meta, push_config, ensure_meta_remote
- forge/pr_merge.rs: tokenised_repo_url delegate + test loosened
- workers/knowledge.rs: clone + push URLs
- socket_server/mod.rs: clone_url in RepoCreated response

No new env var: HIVE_FORGE_URL was already the right knob (mara).

Closes #1868. Closes #2174 (this supersedes the operators-team fix from
the closed #2218, which is re-applied in the ensure_operators_team call
that was already merged separately).

hive-c0re/src/socket_server/mod.rs

@@ -393,7 +393,7 @@ async fn handle_create_repo(agent: &str, repo: &str) -> hive_sh4re::Response {
     };
     match crate::forge::create_agent_repo(agent, repo, &core_token).await {
         Ok(full_name) => hive_sh4re::Response::RepoCreated {
-            clone_url: format!("{}/{full_name}.git", crate::forge::FORGE_HTTP),
+            clone_url: format!("{}/{full_name}.git", crate::forge::forge_http_base()),
             full_name,
         },
         Err(e) => hive_sh4re::Response::Err {