fix: invoke registered command hook only once (#5219)

Remove the duplicate integration hook call before placeholder resolution.

Assisted-by: GitHub Copilot (model: GPT-6.1 Sol, autonomous)

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: mnriem

src/specify_cli/agents.py

@@ -806,11 +806,6 @@ def register_commands(
                     frontmatter, body, source_id=source_id
                 )
 
-            if _integ is not None:
-                frontmatter, body = _integ.process_registered_command(
-                    frontmatter, body, source_id=source_id
-                )
-
             body = self._convert_argument_placeholder(
                 body, "$ARGUMENTS", agent_config["args"]
             )