feat(git identity): one section per git host; CodeCommit SSH key ID makes a plain ssh:// clone work

AWS CodeCommit logs an SSH key in by its IAM SSH key ID (APKA…), so a
plain `git clone ssh://git-codecommit.<region>.amazonaws.com/v1/repos/x`
was refused as the Linux account name. The account can now save an SSH
user per host — PUT/DELETE /api/me/git/ssh-user, listed as `sshUsers` —
written as `url."ssh://<user>@<host>/".insteadOf "ssh://<host>/"` in its
own ~/.gitconfig (as the member under S3), so the plain URL works in a
pane, in Clone and in the git bar. Only rules of exactly that shape are
listed or removed; any other insteadOf is the user's and left alone.

Settings → Git → Your git identity now shows the SSH keys one section
per kind of host, each with only its own numbered steps: GitHub · GitLab
· Gitea · Bitbucket (ED25519) and AWS CodeCommit (RSA: copy → upload in
IAM → paste the key ID and pick the region, then a "Ready" clone line),
plus a collapsed "Other SSH hosts (advanced)". The shared key-type
picker is gone: each section has its own Generate/Replace/Delete.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

server/lib/git-identity.js

@@ -23,7 +23,8 @@
  * A plain `git` typed in a terminal reads none of that, so the account's own
  * `~/.gitconfig` may also carry our `core.sshCommand` (`setTerminalSsh`: on
  * by default for a member, a switch for the host; a user's own is never
- * overwritten).
+ * overwritten), plus a per-host SSH login name (`setSshUser`: AWS CodeCommit
+ * wants the IAM SSH key ID as the user) as a `url.<…>.insteadOf` rule there.
  * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
  */
 
@@ -468,6 +469,79 @@ async function setTerminalSsh(account, on) {
   return terminalSshState(account);
 }
 
+// ── SSH login name per host (`~/.gitconfig` url.<…>.insteadOf) ─────────────
+
+// AWS CodeCommit logs an SSH key in by its IAM key ID (`APKA…`) as the user
+// name, so `ssh://git-codecommit…/v1/repos/x` (no user) is refused. One
+// `url."ssh://<user>@<host>/".insteadOf "ssh://<host>/"` per host makes the
+// plain URL work for every git of the account — a clone typed in a pane, the
+// Clone dialog's and the git bar's — without touching `~/.ssh/config`. The
+// user name is no secret (an ID, not a key), so it may cross sudo's argv.
+const SSH_USER_RE = /^[A-Za-z0-9_][A-Za-z0-9._-]{0,63}$/;
+const insteadOfBase = (host, user) => `ssh://${user}@${host}/`;
+
+/** `[{host, user}]` — only the rules of exactly our shape; any other insteadOf is the user's. */
+async function listSshUsers(account) {
+  const { git } = require("./worktree");
+  const out = await git(homeOf(account), [
+    "config",
+    "--global",
+    "--get-regexp",
+    "^url\\..*\\.insteadof$",
+  ]).then(
+    (r) => r.stdout,
+    () => ""
+  );
+  const rows = [];
+  for (const line of out.split("\n")) {
+    const m = /^url\.ssh:\/\/([^@/\s]+)@([^/\s]+)\/\.insteadof ssh:\/\/([^/\s]+)\/$/.exec(line);
+    if (m && m[2] === m[3] && SSH_USER_RE.test(m[1]) && HOST_RE.test(m[2])) {
+      rows.push({ host: m[2], user: m[1] });
+    }
+  }
+  return rows;
+}
+
+/** Drop our rule for `host` (whatever its user); false when there was none. */
+async function removeSshUser(account, host) {
+  const { git } = require("./worktree");
+  const h = String(host || "").toLowerCase();
+  const rows = (await listSshUsers(account)).filter((r) => r.host === h);
+  for (const r of rows) {
+    await git(homeOf(account), [
+      "config",
+      "--global",
+      "--fixed-value",
+      "--unset-all",
+      `url.${insteadOfBase(r.host, r.user)}.insteadOf`,
+      `ssh://${r.host}/`,
+    ]);
+  }
+  return rows.length > 0;
+}
+
+/** Log in to `host` over SSH as `user` (replaces our earlier rule for that host). */
+async function setSshUser(account, { host, user } = {}) {
+  const h = String(host || "")
+    .trim()
+    .toLowerCase();
+  const u = String(user || "").trim();
+  if (!HOST_RE.test(h)) {
+    throw err("EBADHOST", "a host name like git-codecommit.us-east-1.amazonaws.com");
+  }
+  if (!SSH_USER_RE.test(u)) throw err("EBADSSHUSER", "a user name of letters, digits, . _ -");
+  await removeSshUser(account, h);
+  const { git } = require("./worktree");
+  await git(homeOf(account), [
+    "config",
+    "--global",
+    "--add",
+    `url.${insteadOfBase(h, u)}.insteadOf`,
+    `ssh://${h}/`,
+  ]);
+  return listSshUsers(account);
+}
+
 // ── Network commands in an existing repo (git bar fetch/pull/push) ─────────
 
 /**
@@ -714,6 +788,9 @@ module.exports = {
   terminalSshCommand,
   terminalSshState,
   setTerminalSsh,
+  listSshUsers,
+  setSshUser,
+  removeSshUser,
   listHttps,
   saveHttps,
   removeHttps,