Let error messages stay until read; show the remote form on the welcome screen

Error messages now stay for 8 seconds or until clicked, and keep each
hint on its own line. The welcome screen shows how to start gites with
a repository on another machine. The spec follows these changes and the
new ssh options and socket folder.

docs/superpowers/specs/2026-10-15-remote-repositories-over-ssh-design.md

@@ -35,7 +35,7 @@ one character, and no local folder with exactly that name exists. Every other te
 local folder. So `C:\code\x` and `C:/code/x` stay local, `./a:b` stays local, and a
 folder in the current folder named `notes:2024` stays local when it exists.
 
-A path on the server that starts with `~/` is handed to the server's shell with the
+A path on the server that is `~` or starts with `~/` is handed to the server's shell with the
 `~` outside the quotes, so the shell expands it to the home folder there.
 
 ## Running git
@@ -49,6 +49,7 @@ A path on the server that starts with `~/` is handed to the server's shell with
 
   ```
   ssh -o BatchMode=yes -o ConnectTimeout=10
+      -o ServerAliveInterval=5 -o ServerAliveCountMax=2
       -o ControlMaster=auto -o ControlPath=<socket> -o ControlPersist=10m
       user@myserver "git -C '/srv/app' 'log' '--format=…' …"
   ```
@@ -57,12 +58,18 @@ A path on the server that starts with `~/` is handed to the server's shell with
     has no terminal to ask in. Keys and the ssh agent work.
   - `ConnectTimeout=10`: a server that does not answer gives an error after 10 seconds
     instead of a window that waits for ever.
+  - `ServerAliveInterval=5`, `ServerAliveCountMax=2`: when a server stops answering
+    on a connection that is already open (also a shared one), ssh notices it in about
+    10 seconds and gives an error instead of waiting for ever.
   - `ControlMaster`, `ControlPath`, `ControlPersist`: the first command opens one
     connection and leaves it open; later commands go through it and cost about one
     network round trip each instead of a new login. The connection closes 10 minutes
     after the last command. The socket is `gites-%C` in the user's runtime folder
-    (`/run/user/<id>` on Linux), or in `/tmp` where there is none; `%C` is a hash ssh
-    makes from the host, port and user, so the path stays short.
+    (`/run/user/<id>` on Linux). Where there is none (always on macOS), it is in a
+    `gites` folder in the user's cache folder, made so that only the user can open it;
+    never in `/tmp`. If neither folder can be found or made, these three options are
+    left out and every command opens a new connection. `%C` is a hash ssh makes from
+    the host, port and user, so the path stays short.
   - On Windows, ssh cannot share connections, so these three options are left out and
     every command opens a new connection.
 - Quoting: every word of the git command is put in single quotes, and a `'` inside a
@@ -107,6 +114,12 @@ If the connection drops while a repository is open, the next command shows its e
 as a message at the bottom of the window and the graph that is already on screen
 stays. The next reload connects again by itself.
 
+A message that reports an error stays for 8 seconds, or until it is clicked, and each
+hint line above stays on its own line. Other messages go after 1.8 seconds, as before.
+
+The commands that run git run away from the thread that draws the window, so the
+window does not freeze while it waits for a slow server.
+
 ## Tests
 
 - Reading locations: `host:/path`, `user@host:/path`, `host:~/x`, `C:\x`, `C:/x`, a