Move commit-msg output to `msgs/` subdir

Relocate generated commit message files from
`.claude/` root into `.claude/skills/commit-msg/msgs/`
and switch timestamp format to filesystem-safe UTC
(`%Y%m%dT%H%M%SZ`).

Also,
- add `msgs/` dir and `git_commit_msg_LATEST.md` to
  `.gitignore`.

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

.claude/skills/commit-msg/SKILL.md

@@ -69,13 +69,13 @@ When generating a commit message:
    conventions from the
    [style guide](./style-guide-reference.md).
 4. Add body only for multi-file or complex changes.
-5. Write the message to a file in the repo's
-   `.claude/` subdir with filename format:
-   `<timestamp>_<first-7-chars-of-last-commit-hash>_commit_msg.md`
-   where `<timestamp>` is from `date --iso-8601=seconds`.
-   Also write a copy to
-   `.claude/git_commit_msg_LATEST.md`
-   (overwrite if exists).
+5. Write the message to TWO files:
+   - `.claude/skills/commit-msg/msgs/<timestamp>_<hash>_commit_msg.md`
+     * with `<timestamp>` from `date -u +%Y%m%dT%H%M%SZ`
+       or similar filesystem-safe format.
+     * and `<hash>` from `git log -1 --format=%h`
+       first 7 chars.
+   - `.claude/git_commit_msg_LATEST.md` (overwrite)
 
 ---
 

.gitignore

@@ -107,6 +107,8 @@ ENV/
 .git/
 
 # any commit-msg gen tmp files
+.claude/skills/commit-msg/msgs/
+.claude/git_commit_msg_LATEST.md
 .claude/*_commit_*.md
 .claude/*_commit*.toml