* feat(integrations): add post_process_command_content() hook for all format types
Add post_process_command_content(self, content: str) -> str to IntegrationBase
with a no-op default. Wire it into register_commands() for non-skills format
types (Markdown, TOML, YAML) after format rendering, before writing to disk.
Also applies to aliases rendered via the inject_name path (cline, forge).
Skills-format agents are excluded to preserve the existing
post_process_skill_content() path and avoid double-processing.
This gives extension authors a clean per-agent content transformation seam
for all 21 non-skills integrations that previously had no post-processing hook.
Ref: #3303
Assisted-By: 🤖 Claude Code
* fix: initialize _integration before conditional branch
Prevents potential UnboundLocalError if the non-skills guard is
refactored without updating the alias path reference.
Assisted-By: 🤖 Claude Code
