Add Command Code integration to spec-kit (#4019)

* Add Command Code integration to spec-kit

Adds `command-code` as a built-in skills-based integration so Spec Kit can
be installed into Command Code. Command Code loads agent skills from
`.commandcode/skills/speckit-<name>/SKILL.md` and invokes them in chat as
`$speckit-<command>`.

- New `CommandCodeIntegration` (SkillsIntegration) writing to
  `.commandcode/skills/`; declared multi-install safe (static, isolated
  agent root).
- Register in `_register_builtins()` and the integration catalog.
- Add `command-code` to `DOLLAR_SKILLS_AGENTS` so next-steps guidance
  renders `$speckit-*` invocations.
- Tests: reuse `SkillsIntegrationTests` mixin plus a dollar-invocation
  next-steps test; registry completeness updated.
- Docs: README and docs/reference/integrations.md (supported agents +
  multi-install-safe table).

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>
Assisted-by: Command Code (autonomous)

* Fix issue template agent lists to include command-code

The runtime AGENT_CONFIG now includes command-code, but the GitHub issue
templates and the consistency test's expected key list were not updated,
failing test_issue_template_agent_lists_match_runtime_integrations.

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>
Assisted-by: Command Code (autonomous)

---------

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

src/specify_cli/integrations/__init__.py

@@ -56,6 +56,7 @@ def _register_builtins() -> None:
     from .cline import ClineIntegration
     from .codebuddy import CodebuddyIntegration
     from .codex import CodexIntegration
+    from .command_code import CommandCodeIntegration
     from .copilot import CopilotIntegration
     from .cursor_agent import CursorAgentIntegration
     from .devin import DevinIntegration
@@ -95,6 +96,7 @@ def _register_builtins() -> None:
     _register(ClineIntegration())
     _register(CodebuddyIntegration())
     _register(CodexIntegration())
+    _register(CommandCodeIntegration())
     _register(CopilotIntegration())
     _register(CursorAgentIntegration())
     _register(DevinIntegration())