fix(integrations): use get_invocation_prefix in post_process_skill_content

Replaces the binary is_dollar_skills_agent ternary with get_invocation_prefix
so that Kimi's hook-command note is injected as /skill:speckit-git-commit from
the start. This keeps _inject_hook_command_note idempotent for Kimi: the
previous note with its native prefix now matches on repeated passes, preventing
duplicate note injection.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 65ef91d9-4c31-4f31-a009-ed2093fe7f28
Assisted-by: GitHub Copilot (model: claude-sonnet-4.6, autonomous)

Author: BenBtg

src/specify_cli/integrations/base.py

@@ -27,7 +27,7 @@
 
 import yaml
 
-from .._invocation_style import is_dollar_skills_agent
+from .._invocation_style import get_invocation_prefix, is_dollar_skills_agent
 from .._toml_string import escape_toml_basic as _escape_toml_basic
 from .._toml_string import has_illegal_toml_control as _has_illegal_toml_control
 
@@ -1602,7 +1602,7 @@ def post_process_skill_content(self, content: str) -> str:
         ``$speckit-git-commit``).  Subclasses may override -- see
         ``ClaudeIntegration``.
         """
-        invocation_prefix = "$" if is_dollar_skills_agent(self.key, True) else "/"
+        invocation_prefix = get_invocation_prefix(self.key, True)
         return self._inject_hook_command_note(content, invocation_prefix)
 
     def setup(