✨ Add a skill to rewrite a squashed commit message

The new skill turns HEAD's stacked subjects, bodies and repeated trailers
(a typical result of squashing) into one message that follows
mem:workflow/creating-commits: a single imperative subject, a body
covering the whole branch diff, then the trailers.

It collects every distinct AI-assisted-by value before rewriting, so an
attribution is never dropped, and it requires ./scripts/check-commit to
exit 0 after the amend. It never pushes: rewriting history over commits
the user already pushed is their call, not the agent's.

AI-assisted-by: deepseek-v4.1-flash

.agents/skills/rewrite-commit-message/SKILL.md

@@ -0,0 +1,38 @@
+---
+name: rewrite-commit-message
+description: Rewrite HEAD's commit message (typically a squash that concatenated old messages) into one proper title plus description following Penpot commit conventions, preserving every distinct AI-assisted-by attribution. Amends in place, never pushes.
+slash: true
+---
+
+# Skill: rewrite-commit-message
+
+HEAD's message is a concatenation of older messages (typical after a
+squash): several subjects, bodies and repeated trailers stacked in a
+single message. Replace it with one proper message and amend HEAD.
+
+## When to Use
+
+- The user asks to rewrite, retitle or fix the last commit message
+- After a squash left HEAD with stacked messages and trailer repeats
+
+## Steps
+
+1. Read the full current message (`git log -1 --format=%B HEAD`) and
+   the branch diff (`git diff develop..HEAD --stat`, plus the code
+   when the summary needs grounding).
+2. Collect every DISTINCT `AI-assisted-by:` value in the current
+   message. All of them survive into the new message, one line each:
+   attributions are never dropped in a rewrite, even when most of
+   the old text is.
+3. Draft one message per `mem:workflow/creating-commits` (read it
+   end-to-end first): single subject (imperative, capitalized, no
+   trailing period, ≤80 chars), blank line, body wrapped at ≤80
+   chars covering the whole diff (not the old per-commit slices),
+   then the preserved trailers.
+4. Write it to a file (a heredoc keeps real newlines; inline `-m`
+   with `\n` does not) and `git commit --amend -F <file>`.
+5. Run `./scripts/check-commit` and require exit code 0. A non-zero
+   exit is a hard blocker: fix the message, amend again.
+6. Report the new hash. Never push: the user pushes from their own
+   shell. Warn when local history was rewritten over pushed commits
+   (the push will need force — their call, not yours).