AGENTS: add author-identity git rule for fleet consistency

AGENTS.md

@@ -8,6 +8,7 @@ This file is the canonical reference for cross-cutting AI-agent rules. The CI/CD
 
 - **Default to staging, not committing.** Stage changes with `git add` and leave `git commit` to the developer unless the developer has explicitly authorized the agent to commit for the current ask ("commit this", "open a PR", etc.). Authorization is scope-bound - it covers the commits needed for that specific task, not a blanket commit license for the rest of the session.
 - **All commits must be cryptographically signed (SSH or GPG).** Branch protection enforces this on both branches; unsigned commits are rejected on push. Signing depends on environment configuration - `git config commit.gpgsign true`, a configured `user.signingkey`, and a working signing agent (loaded `ssh-agent` for SSH, or `gpg-agent` for GPG). If signing is not configured in the environment, **do not commit** - surface the missing config to the developer and stop at `git add`. Verify before any agent-authored commit (`git config --get commit.gpgsign && ssh-add -L` or the GPG equivalent). **Signing must be live before the *first* commit, not retrofitted.** Turning on `Require signed commits` against a branch that already has unsigned commits forces a rewrite of that entire history to re-sign it - changing every commit SHA and making whoever does the rewrite the committer and signer of every commit (a rebase preserves the `author` field but not the original signatures; you cannot sign another contributor's commits for them). During new-repo setup, never create commits until signing is verified.
+- **Commit under the committing account's own GitHub `noreply` identity - never a private, personal, or invented address.** The `author` and `committer` on every agent-authored commit are the GitHub `noreply` address of the account whose key signs the commit (above) - GitHub issues these in a `username@users.noreply.github.com` or `ID+username@users.noreply.github.com` form, and for this single-maintainer fleet it is the owner's `ptr727@users.noreply.github.com`. Do not set `user.name`/`user.email` to a fabricated persona, bot name, or product name, and do not commit under whatever identity the environment happens to carry: verify `git config --get user.email` is that GitHub `noreply` address before committing, and fix it if not. A wrong identity is not cosmetic - a private email trips GitHub's email-privacy push protection (GH007), and an unrecognized or invented author pollutes history. Identity is separate from signing: a wrong author does not by itself fail the signature rule, but the ad-hoc identities that produce it are typically also unsigned, which the signing rule above then rejects on push.
 - **Never force push.** Do not run `git push --force` or `git push --force-with-lease` under any circumstances. Force pushing rewrites shared history and can cause data loss.
 - **Never run destructive git commands** (`git reset --hard`, `git checkout .`, `git restore .`, `git clean -f`) without explicit developer instruction.