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>

client/src/lib/api.ts

@@ -2676,6 +2676,11 @@ export const api = {
     /** PUT /api/me/git/ssh-terminal — use the key for git typed in the account's terminal. */
     setTerminalSsh: (on: boolean) =>
       request<GitIdentity>("/me/git/ssh-terminal", { method: "PUT", body: JSON.stringify({ on }) }),
+    /** PUT /api/me/git/ssh-user — the SSH login name for a host (CodeCommit: the SSH key ID). */
+    setSshUser: (body: { host: string; user: string }) =>
+      request<GitIdentity>("/me/git/ssh-user", { method: "PUT", body: JSON.stringify(body) }),
+    removeSshUser: (host: string) =>
+      request<GitIdentity>(`/me/git/ssh-user/${encodeURIComponent(host)}`, { method: "DELETE" }),
     saveHttps: (body: { host: string; username: string; password: string }) =>
       request<GitIdentity>("/me/git/https", { method: "POST", body: JSON.stringify(body) }),
     removeHttps: (host: string) =>
@@ -4210,6 +4215,8 @@ export interface GitIdentity {
   sshKeys?: { type?: "ed25519" | "rsa"; publicKey: string; fingerprint: string }[];
   /** The terminal switch (shared by both keys); null without a key. */
   sshTerminal?: "on" | "off" | "foreign" | null;
+  /** SSH login name per host (`url.<…>.insteadOf` in `~/.gitconfig`); absent from an older server. */
+  sshUsers?: { host: string; user: string }[];
   /** The account's commit author (`git config --global`); null fields = unset. */
   author: { name: string | null; email: string | null };
   https: {