fix: allow Claude to chain skills for hook execution (#2227)

* fix: allow Claude to chain skills for hook execution (#2178)

- Set disable-model-invocation to false so Claude can invoke extension
  skills (e.g. speckit-git-feature) from within workflow skills
- Inject dot-to-hyphen normalization note into Claude SKILL.md hook
  sections so the model maps extension.yml command names to skill names
- Replace Unicode checkmark with ASCII [OK] in auto-commit scripts to
  fix PowerShell encoding errors on Windows
- Move Claude-specific frontmatter injection to ClaudeIntegration via
  post_process_skill_content() hook on SkillsIntegration, wired through
  presets and extensions managers
- Add positive and negative tests for all changes

Fixes #2178

* refactor: address PR review feedback

- Preserve line-ending style (CRLF/LF) in _inject_hook_command_note
  instead of always inserting \n, matching the convention used by other
  injection helpers in the same module.

- Extract duplicated _post_process_skill() from extensions.py and
  presets.py into a shared post_process_skill() function in agents.py.
  Both modules now import and call the shared helper.

* fix: match full hook instruction line in regex

The regex in _inject_hook_command_note only matched lines ending
immediately after 'output the following', but the actual template
lines continue with 'based on its `optional` flag:'. Use [^\r\n]*
to capture the rest of the line before the EOL.

* refactor: use integration object directly for post_process_skill_content

Instead of a free function in agents.py that re-resolves the
integration by key, callers in extensions.py and presets.py now
resolve the integration once via get_integration() and call
integration.post_process_skill_content() directly. The base
identity method lives on SkillsIntegration.