feat(integrations): add Grok Build skills-based integration (#3535)

* feat(integrations): add Grok Build skills-based integration

Add first-class support for xAI Grok Build via SkillsIntegration, installing
speckit skills under .grok/skills and wiring init/invocation/catalog surfaces.

Assisted-by: Grok Build (model: grok-4, supervised)

* test+docs: address Copilot review on Grok multi-install and next steps

Assert init next-steps guidance for Grok (.grok/skills, /speckit-*) and
clarify that multi-install safety is path/manifest isolation, not
agent-context defaults such as shared AGENTS.md.

* fix(integrations): Grok headless --always-approve and isolation paths

Document Grok multi-install isolation as .grok/skills and .grok/rules.
Override build_exec_args to pass --always-approve so non-interactive
dispatch is not blocked at tool permission gates.

* docs(integrations): list only managed .grok/skills for Grok isolation

Multi-install isolation documents Spec Kit-managed paths; Grok only
writes .grok/skills, so drop the read-only .grok/rules entry.

* fix(integrations): always-slash Grok hooks and refresh catalog date

Move grok to ALWAYS_SLASH_AGENTS so hooks never emit /speckit.plan when
ai_skills is missing/false. Update slash-format tests, persist ai_skills
on init, and bump catalog updated_at for the Grok entry.

---------

Co-authored-by: Nate Chadwick <1232206+natechadwick@users.noreply.github.com>
Co-authored-by: test <test@example.com>

src/specify_cli/integrations/__init__.py

@@ -63,6 +63,7 @@ def _register_builtins() -> None:
     from .gemini import GeminiIntegration
     from .generic import GenericIntegration
     from .goose import GooseIntegration
+    from .grok import GrokIntegration
     from .hermes import HermesIntegration
     from .junie import JunieIntegration
     from .kilocode import KilocodeIntegration
@@ -99,6 +100,7 @@ def _register_builtins() -> None:
     _register(GeminiIntegration())
     _register(GenericIntegration())
     _register(GooseIntegration())
+    _register(GrokIntegration())
     _register(HermesIntegration())
     _register(JunieIntegration())
     _register(KilocodeIntegration())