fix(codex): inject dot-to-hyphen hook command note in Codex skills (#2503)

* fix(codex): inject dot-to-hyphen hook command note in Codex skills

Hook commands in `.specify/extensions.yml` use dotted ids like
`speckit.git.commit`, but Codex skills are named with hyphens
(`speckit-git-commit`). The Claude integration handles this via an
explicit instruction injected into each generated SKILL.md by
`ClaudeIntegration.post_process_skill_content`, but the Codex
integration had no such override, so Codex would emit
`/speckit.git.commit` (which does not resolve) instead of
`/speckit-git-commit`.

This adds the same `_inject_hook_command_note` helper and a
`post_process_skill_content` override to `CodexIntegration`, plus a
small `setup()` override that applies the post-process to each
generated SKILL.md (mirroring the pattern in `ClaudeIntegration`).

Also widens the existing
`test_non_claude_post_process_is_identity` test to use `agy`
(another `SkillsIntegration` with no override), since asserting
identity behavior on Codex would now incorrectly fail.

Tests:
- New `TestCodexHookCommandNote` class mirrors
  `TestClaudeHookCommandNote`: setup-level injection, no-op when
  no hook block is present, idempotency, and indentation
  preservation.
- `pytest tests/` → 2866 passed, 34 skipped.

Signed-off-by: Chao Zhang <1175468+picklebento@users.noreply.github.com>

* fix(codex): handle empty eol when instruction is final line without newline

The hook-note injection regex allowed end-of-string matches via ``$``,
which left the captured ``eol`` empty. When the matched indent was also
empty, the substitution concatenated the note onto the same line as the
instruction. Default ``eol`` to ``\n`` when the capture is empty.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

---------

Signed-off-by: Chao Zhang <1175468+picklebento@users.noreply.github.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>