Add the bind-commit agent skill

Walk agents through the full commit workflow: the git-clang-format
staging sequence, reason-focused messages hard-wrapped at 72 columns
with no type prefixes, the Assisted-by trailer and the forbidden ones,
amend and fixup discipline for HEAD and non-HEAD commits, and the rule
that agents commit locally and leave publishing to the user.

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+---
+name: bind-commit
+description: The full commit workflow for BIND 9 repositories — pre-commit clang-format sequence, message shape and 72-column wrapping, trailer rules (Assisted-by and the forbidden ones), amend/fixup discipline, and the never-push boundary. Use EVERY time you are about to create, amend, reword, or fix up a commit in any BIND 9 checkout.
+---
+
+# Committing to BIND 9 — the full checklist
+
+## Pre-commit formatting (C files)
+
+1. `git add <files>`
+2. `git-clang-format HEAD` — the hyphenated binary. `git clang-format`
+   (with a space) invokes a nonexistent git subcommand and fails. It
+   operates on STAGED files only.
+3. `git add` any reformatted files, then commit.
+
+Only format C lines you wrote or edited yourself. If the working-tree
+diff was authored by the user (their editor, their patch), do NOT run
+clang-format over it — it is not your code to reformat.
+
+## Message shape
+
+- ≤3 paragraphs; a single short paragraph is usually enough. Focus on
+  WHY — the reviewer can read the diff. Never narrate the diff or
+  enumerate per-function before/after behavior ("Gosh the commit
+  message is so long and chatty").
+- Plain subject, no `new:`/`fix:`/`dev:`/`doc:` prefix — those appear
+  only on GitLab-generated MR-merge commits. Real branch-commit style:
+  `git log --no-merges --first-parent`.
+- Hard-wrap the body at ~72 columns. `git commit -m` does NOT wrap: a
+  long paragraph becomes one unwrapped line that sticks out
+  immediately. Write the message pre-wrapped to a file and use
+  `git commit -F <file>`, or pass each physical line as its own `-m`.
+
+## Trailers
+
+- `Assisted-by: <tool>:<model-id>` (model id from the runtime
+  environment, e.g. `claude-fable-5`) ONLY when LLM wrote the
+  load-bearing code/test/config content of the commit. NOT for:
+  rewording a message, squashing fixups, review-only advice, or a
+  comment/doc block added around a user-authored fix — a comment is
+  prose, not the fix; do not rationalize "the comment was AI" to keep
+  the trailer.
+- After the model id, list specialized analysis tools actually used
+  (coccinelle, clang-tidy, AFL, Coverity, fuzzers) — never trivial
+  tooling (git, compilers, meson, clang-format, black, ruff).
+- NEVER, in any repo:
+  - `Co-Authored-By: ...` or any AI co-author line;
+  - `Signed-off-by:` from the agent (it cannot certify the DCO);
+  - `Closes #N` / `Fixes #N` / `Refs #N` — issue refs go in the MR
+    description; the branch name already encodes the issue number;
+
+## Amending
+
+- HEAD, polish-only (typo, message tightening, whitespace): plain
+  `--amend`; keep the original author (git's default).
+- HEAD, implementation replaced by a different approach:
+  `--amend --reset-author` (or explicit `--author=`) — attribution
+  follows whoever wrote the NEW code, not whoever wrote the discarded
+  version. When in doubt about amending someone else's commit, ask
+  first. The Assisted-by question is independent — re-derive it from
+  who authored the new content.
+- NOT HEAD: NEVER rebuild the branch with `git reset --hard <older>` +
+  cherry-pick (this once collided with the user's concurrent rebase and
+  trashed the branch). Instead add a fixup commit on top:
+  - content (and message): `git commit --fixup=amend:<hash>`
+  - message only: `git commit --fixup=reword:<hash>` — it opens an
+    editor and ignores `-m`; supply the wrapped message via
+    `GIT_EDITOR='cp /path/to/msg.txt'`
+  - content only, keep message: `git commit --fixup=<hash>`
+
+  Then STOP and hand `git rebase -i --autosquash <base>` to the user —
+  never run the rebase yourself.
+- Before ANY history operation run `git status`; if a rebase or
+  cherry-pick is in progress, do not touch the branch.
+
+## The boundary
+
+Commit locally only. Never `git push` (any variant), never
+`gh pr create` / `glab mr create`. When the work is finished, hand the
+MR title/description over as text (see the bind-mr-description skill)
+— do not offer to push or open the MR.