feat(integrations): generalize post-processing to all format types (#3311)

* 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

src/specify_cli/integrations/base.py

@@ -123,6 +123,19 @@ class IntegrationBase(ABC):
     integration that sets this flag.
     """
 
+    def post_process_command_content(self, content: str) -> str:
+        """Transform command content after format rendering.
+
+        Called by ``register_commands()`` for non-skills format types
+        (Markdown, TOML, YAML) after the command has been rendered into
+        its target format and before writing to disk.  Skills-format
+        agents use ``post_process_skill_content()`` instead.
+
+        Subclasses may override to inject agent-specific content.
+        The default implementation returns *content* unchanged.
+        """
+        return content
+
     # -- Public API -------------------------------------------------------
 
     @classmethod